1.
Fluorescence
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Fluorescence is the emission of light by a substance that has absorbed light or other electromagnetic radiation. It is a form of luminescence, in most cases, the emitted light has a longer wavelength, and therefore lower energy, than the absorbed radiation. Fluorescent materials cease to glow immediately when the radiation source stops, unlike phosphorescence, Fluorescence also occurs frequently in nature in some minerals and in various biological states in many branches of the animal kingdom. An early observation of fluorescence was described in 1560 by Bernardino de Sahagún and it was derived from the wood of two tree species, Pterocarpus indicus and Eysenhardtia polystachya. The chemical compound responsible for this fluorescence is matlaline, which is the product of one of the flavonoids found in this wood. The name was derived from the fluorite, some examples of which contain traces of divalent europium. In a key experiment he used a prism to isolate ultraviolet radiation from sunlight, the specific frequencies of exciting and emitted light are dependent on the particular system. S0 is called the state of the fluorophore, and S1 is its first excited singlet state. A molecule in S1 can relax by various competing pathways and it can undergo non-radiative relaxation in which the excitation energy is dissipated as heat to the solvent. Excited organic molecules can also relax via conversion to a triplet state, relaxation from S1 can also occur through interaction with a second molecule through fluorescence quenching. Molecular oxygen is an extremely efficient quencher of fluorescence just because of its unusual triplet ground state, in most cases, the emitted light has a longer wavelength, and therefore lower energy, than the absorbed radiation, this phenomenon is known as the Stokes shift. The emitted radiation may also be of the wavelength as the absorbed radiation. Molecules that are excited through light absorption or via a different process can transfer energy to a second sensitized molecule, the fluorescence quantum yield gives the efficiency of the fluorescence process. It is defined as the ratio of the number of photons emitted to the number of photons absorbed, Φ = Number of photons emitted Number of photons absorbed The maximum fluorescence quantum yield is 1.0, each photon absorbed results in a photon emitted. Compounds with quantum yields of 0.10 are still considered quite fluorescent, thus, if the rate of any pathway changes, both the excited state lifetime and the fluorescence quantum yield will be affected. Fluorescence quantum yields are measured by comparison to a standard, the quinine salt quinine sulfate in a sulfuric acid solution is a common fluorescence standard. The fluorescence lifetime refers to the time the molecule stays in its excited state before emitting a photon. This is an instance of exponential decay, various radiative and non-radiative processes can de-populate the excited state
2.
Polymer
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A polymer is a large molecule, or macromolecule, composed of many repeated subunits. Because of their range of properties, both synthetic and natural polymers play an essential and ubiquitous role in everyday life. Polymers range from familiar synthetic plastics such as polystyrene to natural biopolymers such as DNA and proteins that are fundamental to biological structure, Polymers, both natural and synthetic, are created via polymerization of many small molecules, known as monomers. The units composing polymers derive, actually or conceptually, from molecules of low molecular mass. The term was coined in 1833 by Jöns Jacob Berzelius, though with a distinct from the modern IUPAC definition. The modern concept of polymers as covalently bonded macromolecular structures was proposed in 1920 by Hermann Staudinger, Polymers are studied in the fields of biophysics and macromolecular science, and polymer science. Polyisoprene of latex rubber is an example of a polymer. In biological contexts, essentially all biological macromolecules—i. e, proteins, nucleic acids, and polysaccharides—are purely polymeric, or are composed in large part of polymeric components—e. g. Isoprenylated/lipid-modified glycoproteins, where small molecules and oligosaccharide modifications occur on the polyamide backbone of the protein. The simplest theoretical models for polymers are ideal chains, Polymers are of two types, Natural polymeric materials such as shellac, amber, wool, silk and natural rubber have been used for centuries. A variety of natural polymers exist, such as cellulose. Most commonly, the continuously linked backbone of a used for the preparation of plastics consists mainly of carbon atoms. A simple example is polyethylene, whose repeating unit is based on ethylene monomer, however, other structures do exist, for example, elements such as silicon form familiar materials such as silicones, examples being Silly Putty and waterproof plumbing sealant. Oxygen is also present in polymer backbones, such as those of polyethylene glycol, polysaccharides. Polymerization is the process of combining many small molecules known as monomers into a covalently bonded chain or network, during the polymerization process, some chemical groups may be lost from each monomer. This is the case, for example, in the polymerization of PET polyester, the distinct piece of each monomer that is incorporated into the polymer is known as a repeat unit or monomer residue. Laboratory synthetic methods are divided into two categories, step-growth polymerization and chain-growth polymerization. However, some methods such as plasma polymerization do not fit neatly into either category
3.
Thiophene
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Thiophene, also commonly called thiofuran, is a heterocyclic compound with the formula C4H4S. Consisting of a flat five-membered ring, it is aromatic as indicated by its extensive substitution reactions, related to thiophene are benzothiophene and dibenzothiophene, containing the thiophene ring fused with one and two benzene rings, respectively. Compounds analogous to thiophene include furan and pyrrole, which vary by the heteroatom in the ring. Thiophene was discovered as a contaminant in benzene and it was observed that isatin forms a blue dye if it is mixed with sulfuric acid and crude benzene. The formation of the blue indophenin had long believed to be a reaction of benzene itself. Viktor Meyer was able to isolate thiophene as the substance responsible for this reaction. Thiophene and its derivatives occur in petroleum, sometimes in concentrations up to 1–3%, the thiophenic content of oil and coal is removed via the hydrodesulfurization process. In HDS, the liquid or gaseous feed is passed over a form of molybdenum disulfide catalyst under a pressure of H2, thiophenes undergo hydrogenolysis to form hydrocarbons and hydrogen sulfide. Thus, thiophene itself is converted to butane and H2S, more prevalent and more problematic in petroleum are benzothiophene and dibenzothiophene. Thiophenes are classically prepared by the reaction of 1, 4-diketones, diesters, another method is the Volhard–Erdmann cyclization. Thiophene is produced on a scale of around 2,000,000 kilograms per year worldwide, production involves the vapor phase reaction of a sulfur source, typically carbon disulfide, and butanol. These reagents are contacted with an oxide catalyst at 500–550 °C, at room temperature, thiophene is a colorless liquid with a mildly pleasant odor reminiscent of benzene, with which thiophene shares some similarities. The high reactivity of thiophene toward sulfonation is the basis for the separation of thiophene from benzene, like benzene, thiophene forms an azeotrope with ethanol. The molecule is flat, the angle at the sulphur is around 93°, the C–C–S angle is around 109°. The C–C bonds to the adjacent to the sulphur are about 1.34 Å, the C–S bond length is around 1.70 Å. Thiophene is considered to be aromatic, although theoretical calculations suggest that the degree of aromaticity is less than that of benzene, the electron pairs on sulfur are significantly delocalized in the pi electron system. As a consequence of its aromaticity, thiophene does not exhibit the properties seen for conventional thioethers, for example, the sulfur atom resists alkylation and oxidation. In these cases oxidation can occur both at sulfur, giving a thiophene S-oxide, as well as at the 2, 3-double bond, giving the thiophene 2, 3-epoxide, oxidation of thiophene by trifluoroperacetic acid also demonstrates both reaction pathways
4.
Sulfur
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Sulfur or sulphur is a chemical element with symbol S and atomic number 16. It is abundant, multivalent, and nonmetallic, under normal conditions, sulfur atoms form cyclic octatomic molecules with chemical formula S8. Elemental sulfur is a yellow crystalline solid at room temperature. Chemically, sulfur reacts with all elements except for gold, platinum, iridium, tellurium, though sometimes found in pure, native form, sulfur usually occurs as sulfide and sulfate minerals. Being abundant in native form, sulfur was known in ancient times, being mentioned for its uses in ancient India, ancient Greece, China, in the Bible, sulfur is called brimstone. Today, almost all elemental sulfur is produced as a byproduct of removing sulfur-containing contaminants from natural gas, the greatest commercial use of the element is the production of sulfuric acid for sulfate and phosphate fertilizers, and other chemical processes. The element sulfur is used in matches, insecticides, and fungicides, many sulfur compounds are odoriferous, and the smells of odorized natural gas, skunk scent, grapefruit, and garlic are due to organosulfur compounds. Hydrogen sulfide gives the characteristic odor to rotting eggs and other biological processes, sulfur is an essential element for all life, but almost always in the form of organosulfur compounds or metal sulfides. Three amino acids and two vitamins are organosulfur compounds, many cofactors also contain sulfur including glutathione and thioredoxin and iron–sulfur proteins. Disulfides, S–S bonds, confer mechanical strength and insolubility of the keratin, found in outer skin, hair. Sulfur is one of the chemical elements needed for biochemical functioning and is an elemental macronutrient for all organisms. Sulfur is derived from the Latin word sulpur, which was Hellenized to sulphur, the spelling sulfur appears toward the end of the Classical period. In 12th-century Anglo-French, it was sulfre, in the 14th century the Latin ph was restored, for sulphre, the parallel f~ph spellings continued in Britain until the 19th century, when the word was standardized as sulphur. Sulfur was the form chosen in the United States, whereas Canada uses both, the IUPAC adopted the spelling sulfur in 1990, as did the Nomenclature Committee of the Royal Society of Chemistry in 1992, restoring the spelling sulfur to Britain. Sulfur forms polyatomic molecules with different chemical formulas, the best-known allotrope being octasulfur, cyclo-S8. The point group of cyclo-S8 is D4d and its dipole moment is 0 D. Octasulfur is a soft, bright-yellow solid that is odorless and it melts at 115.21 °C, boils at 444.6 °C and sublimes easily. At 95.2 °C, below its melting temperature, cyclo-octasulfur changes from α-octasulfur to the β-polymorph, the structure of the S8 ring is virtually unchanged by this phase change, which affects the intermolecular interactions. At higher temperatures, the viscosity decreases as depolymerization occurs, molten sulfur assumes a dark red color above 200 °C
5.
Heterocyclic compound
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A heterocyclic compound or ring structure is a cyclic compound that has atoms of at least two different elements as members of its ring. Heterocyclic chemistry is the branch of chemistry dealing with the synthesis, properties. Examples of heterocyclic compounds include all of the acids, the majority of drugs, most biomass. Although heterocyclic compounds may be inorganic, most contain at least one carbon, while atoms that are neither carbon nor hydrogen are normally referred to in organic chemistry as heteroatoms, this is usually in comparison to the all-carbon backbone. But this does not prevent a compound such as borazine from being labelled heterocyclic, IUPAC recommends the Hantzsch-Widman nomenclature for naming heterocyclic compounds. Heterocyclic compounds can be classified based on their electronic structure. The saturated heterocycles behave like the acyclic derivatives, thus, piperidine and tetrahydrofuran are conventional amines and ethers, with modified steric profiles. Therefore, the study of heterocyclic chemistry focuses especially on unsaturated derivatives, included are pyridine, thiophene, pyrrole, and furan. Another large class of heterocycles are fused to rings, which for pyridine, thiophene, pyrrole, and furan are quinoline, benzothiophene, indole. Fusion of two benzene rings gives rise to a large family of compounds, respectively the acridine, dibenzothiophene, carbazole. The unsaturated rings can be classified according to the participation of the heteroatom in the pi system, heterocycles with three atoms in the ring are more reactive because of ring strain. Those containing one heteroatom are, in general, stable and those with two heteroatoms are more likely to occur as reactive intermediates. Five-membered rings with one heteroatom, The 5-membered ring compounds containing two heteroatoms, at least one of which is nitrogen, are called the azoles. Thiazoles and isothiazoles contain a sulfur and an atom in the ring. A large group of 5-membered ring compounds with three heteroatoms also exists, one example is dithiazoles that contain two sulfur and a nitrogen atom. Five-member ring compounds with four heteroatoms, With 5-heteroatoms, the compound may be considered rather than heterocyclic. With 7-membered rings, the heteroatom must be able to provide an empty pi orbital for normal aromatic stabilization to be available, otherwise, for example, with the benzo-fused unsaturated nitrogen heterocycles, pyrrole provides indole or isoindole depending on the orientation. The pyridine analog is quinoline or isoquinoline, for azepine, benzazepine is the preferred name
6.
Conductive polymer
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Conductive polymers or, more precisely, intrinsically conducting polymers are organic polymers that conduct electricity. Such compounds may have metallic conductivity or can be semiconductors, the biggest advantage of conductive polymers is their processability, mainly by dispersion. Conductive polymers are generally not thermoplastics, i. e. they are not thermoformable, but, like insulating polymers, they are organic materials. They can offer high electrical conductivity but do not show similar mechanical properties to other commercially available polymers, the electrical properties can be fine-tuned using the methods of organic synthesis and by advanced dispersion techniques. Polyaniline was first described in the century by Henry Letheby. He noted that reduced form was colourless but the forms were deep blue. The first highly-conductive organic compounds were the charge transfer complexes, in the 1950s, researchers reported that polycyclic aromatic compounds formed semi-conducting charge-transfer complex salts with halogens. In 1954, researchers at Bell Labs and elsewhere reported organic charge transfer complexes with resistivities as low as 8 ohms-cm, in the early 1970s, researchers demonstrated salts of tetrathiafulvalene show almost metallic conductivity, while superconductivity was demonstrated in 1980. Broad research on charge transfer salts continues today, while these compounds were technically not polymers, this indicated that organic compounds can carry current. While organic conductors were previously intermittently discussed, the field was particularly energized by the prediction of superconductivity following the discovery of BCS theory, in 1963 Australians B. A. Bolto, D. E. Weiss, and coworkers reported derivatives of polypyrrole with resistivities as low as 1 ohm·cm, cites multiple reports of similar high-conductivity oxidized polyacetylenes. With the notable exception of charge transfer complexes, organic molecules were previously considered insulators or at best weakly conducting semiconductors, subsequently, DeSurville and coworkers reported high conductivity in a polyaniline. Likewise, in 1980, Diaz and Logan reported films of polyaniline that can serve as electrodes, while mostly operating in the quantum realm of less than 100 nanometers, molecular electronic processes can collectively manifest on a macro scale. Examples include quantum tunneling, negative resistance, phonon-assisted hopping and polarons, in 1977, Alan J. Heeger, Alan MacDiarmid and Hideki Shirakawa reported similar high conductivity in oxidized iodine-doped polyacetylene. For this research, they were awarded the 2000 Nobel Prize in Chemistry for the discovery, polyacetylene itself did not find practical applications, but drew the attention of scientists and encouraged the rapid growth of the field. Since the late 1980s, organic light-emitting diodes have emerged as an important application of conducting polymers, the linear-backbone polymer blacks and their copolymers are the main class of conductive polymers. Poly and its derivatives have emerged as the prototypical electroluminescent semiconducting polymers. Today, poly are the materials for solar cells and transistors
7.
Nobel Prize in Chemistry
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The Nobel Prize in Chemistry is awarded annually by the Royal Swedish Academy of Sciences to scientists in the various fields of chemistry. It is one of the five Nobel Prizes established by the will of Alfred Nobel in 1895, awarded for outstanding contributions in chemistry, physics, literature, peace, and physiology or medicine. This award is administered by the Nobel Foundation and awarded by Royal Swedish Academy of Sciences on proposal of the Nobel Committee for Chemistry which consists of five elected by Academy. The award is presented in Stockholm at a ceremony on December 10. The first Nobel Prize in Chemistry was awarded in 1901 to Jacobus Henricus van t Hoff, of the Netherlands, for his discovery of the laws of chemical dynamics and osmotic pressure in solutions. From 1901 to 2016, the award has been bestowed on a total of 174 individuals, though Nobel wrote several wills during his lifetime, the last was written a little over a year before he died, and signed at the Swedish-Norwegian Club in Paris on 27 November 1895. Nobel bequeathed 94% of his assets,31 million Swedish kronor, to establish. Due to the level of surrounding the will, it was not until April 26,1897 that it was approved by the Storting. The executors of his will were Ragnar Sohlman and Rudolf Lilljequist, the members of the Norwegian Nobel Committee that were to award the Peace Prize were appointed shortly after the will was approved. The prize-awarding organisations followed, the Karolinska Institutet on June 7, the Swedish Academy on June 9, the Nobel Foundation then reached an agreement on guidelines for how the Nobel Prize should be awarded. In 1900, the Nobel Foundations newly created statutes were promulgated by King Oscar II, according to Nobels will, The Royal Swedish Academy of Sciences were to award the Prize in Chemistry. The committee and institution serving as the board for the prize typically announce the names of the laureates in October. The prize is awarded at formal ceremonies held annually on December 10. The highlight of the Nobel Prize Award Ceremony in Stockholm is when each Nobel Laureate steps forward to receive the prize from the hands of His Majesty the King of Sweden, the Nobel Laureate receives three things, a diploma, a medal and a document confirming the prize amount. Later the Nobel Banquet is held in Stockholm City Hall, a maximum of three laureates and two different works may be selected. The award can be given to a maximum of three recipients per year and it consists of a gold medal, a diploma, and a cash grant. The Nobel Laureates in chemistry are selected by a committee that consists of five elected by the Royal Swedish Academy of Sciences. In its first stage, several people are asked to nominate candidates
8.
Alan J. Heeger
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Alan Jay Heeger is an American physicist, academic and Nobel Prize laureate in chemistry. Heeger was born in Sioux City, Iowa, to a Jewish family and he grew up in Akron, Iowa, where his father owned a general store. At age nine, following his fathers death, the moved to Sioux City. Heeger earned a B. S. in physics and mathematics from the University of Nebraska-Lincoln in 1957, from 1962 to 1982 he was on the faculty of the University of Pennsylvania. In 1982 he commenced his present appointment as a professor in the Physics Department and his research has led to the formation of numerous start-up companies including Uniax, Konarka, and Sirigen, founded in 2003 by Guillermo C. Bazan, Patrick J. Dietzen, Brent S. Gaylord, alan Heeger was a founder of Uniax, which was acquired by DuPont. His sons are the neuroscientist David Heeger and the immunologist Peter Heeger, Heeger is also a member of the USA Science and Engineering Festivals Advisory Board. Heeger has been a judge of the STAGE International Script Competition three times and this process is the essence of creativity in science. I have been fortunate to have experienced this intense pleasure many times in my life, alan J Heeger, Never Lose Your Nerve
9.
Alan MacDiarmid
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Alan Graham MacDiarmid, ONZ FRS was a New Zealand-born American chemist, and one of three recipients of the Nobel Prize for Chemistry in 2000. MacDiarmid was born in Masterton, New Zealand as one of five children – three brothers and two sisters. His family was poor, and the Great Depression made life difficult in Masterton, due to which his family shifted to Lower Hutt. At around age ten, he developed an interest in chemistry from one of his fathers old textbooks, MacDiarmid was educated at Hutt Valley High School and Victoria University of Wellington. In 1943, MacDiarmid passed the University of New Zealands University Entrance Exam and he then took up a part-time job as a lab boy or janitor in Victoria University of Wellington, during his studies for a BSc degree, which he completed in 1947. He was then appointed demonstrator in the undergraduate laboratories, after completing an MSc in chemistry from the same university, he later worked as an assistant in its chemistry department. It was here that he had his first publication in 1949 and he graduated in 1951 with first class honours, and won a Fulbright Fellowship to the University of Wisconsin–Madison. He majored in chemistry, receiving his M. S. degree in 1952. He then won a Shell Graduate Scholarship, which enabled him to go to Sidney Sussex College, Cambridge, MacDiarmid worked in the School of Chemistry at the University of St Andrews in Scotland for a year as a member of the junior faculty. He then took a faculty position in chemistry at the University of Pennsylvania, USA, MacDiarmid spent the greater part of his career on the chemistry faculty of the University of Pennsylvania, where he worked for 45 years. The first twenty years of his research focused on silicon chemistry. He was appointed Blanchard Professor of Chemistry in 1988, in 2002 MacDiarmid also joined the faculty of the University of Texas at Dallas. His best-known research was the discovery and development of conductive materials that conduct electricity. He collaborated with the Japanese chemist Hideki Shirakawa and the American physicist Alan Heeger in this research, the three of them shared the 2000 Nobel Prize in Chemistry for this work. The Nobel Prize was awarded for the discovery that plastics can, after certain modifications, the work progressed to yield important practical applications. Conductive plastics can be used for anti-static substances for photographic film, semi-conductive polymers have been applied in light-emitting diodes, solar cells and displays in mobile telephones. Future developments in electronics are predicted to dramatically increase the speed while reducing the size of computers. MacDiarmid also travelled around the world for speaking engagements that impressed upon listeners the value of globalising the effort of innovation in the 21st century, in one of his last courses, in 2001, MacDiarmid elected to lead a small seminar of incoming freshmen about his research activities
10.
Hideki Shirakawa
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1936 Born in Tokyo, in the family of a military doctor. Around third grade, he moved to Takayama, Gifu, which is the hometown of his mother,1961 Graduated from Tokyo Institute of Technology, Chemical engineering department in the School of Science and Engineering. 1966 Received doctorate from Chemical engineering department in Graduate School of Science, obtained the post of assistant in Chemical Resources Laboratory at Tokyo Tech. 1976 Post-doctoral researcher in the University of Pennsylvania, USA with invitation by Alan MacDiarmid and this result interested Alan MacDiarmid when MacDiarmid visited TITech in 1975. In 1976, he was invited to work in the laboratory of Alan MacDiarmid as a fellow at the University of Pennsylvania. The two developed the electrical conductivity of polyacetylene along with American physicist Alan Heeger, in 1977 they discovered that doping with iodine vapor could enhance the conductivity of polyacetylene. The three scientists were awarded the Nobel Prize in Chemistry in 2000 in recognition of the discovery, with regard to the mechanism of electric conduction, it is strongly believed that nonlinear excitations in the form of solitons play a role. He is also related to Naoko Takahashi, the marathon gold medalist of the 2000 Summer Olympics. List of Japanese Nobel laureates Biographical snapshots, Hideki Shirakawa, Journal of Chemical Education web site, Shirakawa, H. Nobel Lecture, The discovery of polyacetylene film-the dawning of an era of conducting polymers. Nobel Prize Biography Nobel Prize Lecture Official Homepage in Japanese Alan MacDiarmid on Winning
11.
Electrical resistivity and conductivity
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Electrical resistivity is an intrinsic property that quantifies how strongly a given material opposes the flow of electric current. A low resistivity indicates a material that allows the flow of electric current. Resistivity is commonly represented by the Greek letter ρ, the SI unit of electrical resistivity is the ohm-metre. Electrical conductivity or specific conductance is the reciprocal of electrical resistivity and it is commonly represented by the Greek letter σ, but κ or γ are also occasionally used. Its SI unit is siemens per metre and CGSE unit is reciprocal second, many resistors and conductors have a uniform cross section with a uniform flow of electric current, and are made of one material. All copper wires, irrespective of their shape and size, have approximately the same resistivity, every material has its own characteristic resistivity – for example, resistivity of rubber is far larger than coppers. If the pipes are the size and shape, the pipe full of sand has higher resistance to flow. Resistance, however, is not solely determined by the presence or absence of sand and it also depends on the length and width of the pipe, short or wide pipes have lower resistance than narrow or long pipes. The above equation can be transposed to get Pouillets law, R = ρ ℓ A, the resistance of a given material increases with length, but decreases with increasing cross-sectional area. From the above equations, resistivity has the SI unit ohm metre, the formula R = ρ ℓ / A can be used to intuitively understand the meaning of a resistivity value. For example, if A = 7000100000000000000♠1 m2 ℓ = 7000100000000000000♠1 m, Conductivity, σ, is defined as the inverse of resistivity, σ =1 ρ. Conductivity has SI units of siemens per metre, the above definition was specific to resistors or conductors with a uniform cross-section, where current flows uniformly through them. A more basic and general definition starts from the fact that a field inside a material makes electric current flow. Conductivity is the inverse, σ =1 ρ = J E, for example, rubber is a material with large ρ and small σ—because even a very large electric field in rubber makes almost no current flow through it. On the other hand, copper is a material with small ρ, according to elementary quantum mechanics, electrons in an atom do not take on arbitrary energy values. Rather, electrons only occupy discrete energy levels in an atom or crystal. When a large number of such allowed energy levels are spaced close together —i. e. have similar energies— we can talk about these energy levels together as an energy band. There can be many such bands in a material, depending on the atomic number
12.
Delocalized electron
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In chemistry, delocalized electrons are electrons in a molecule, ion or solid metal that are not associated with a single atom or a covalent bond. The term is general and can have different meanings in different fields. In organic chemistry, this refers to resonance in conjugated systems, in solid-state physics, this refers to free electrons that facilitate electrical conduction. In quantum chemistry, this refers to molecular orbitals that extend over several adjacent atoms, in the simple aromatic ring of benzene the delocalization of six π electrons over the C6 ring is often graphically indicated by a circle. The fact that the six C-C bonds are equidistant is one indication of this delocalization, in valence bond theory, delocalization in benzene is represented by resonance structures. Delocalized electrons also exist in the structure of solid metals, metallic structure consists of aligned positive ions in a sea of delocalized electrons. This means that the electrons are free to move throughout the structure, in diamond all four outer electrons of each carbon atom are localized between the atoms in covalent bonding. The movement of electrons is restricted and diamond does not conduct an electric current, in graphite, each carbon atom uses only 3 of its 4 outer energy level electrons in covalently bonding to three other carbon atoms in a plane. Each carbon atom contributes one electron to a system of electrons that is also a part of the chemical bonding. The delocalized electrons are free to move throughout the plane, for this reason, graphite conducts electricity along the planes of carbon atoms, but does not conduct in a direction at right angles to the plane. Standard ab initio quantum chemistry methods lead to delocalized orbitals that, in general, localized orbitals may then be found as linear combinations of the delocalized orbitals, given by an appropriate unitary transformation. In the methane molecule for example, ab initio calculations show bonding character in four molecular orbitals, there are two orbital levels, a bonding molecular orbital formed from the 2s orbital on carbon and triply degenerate bonding molecular orbitals from each of the 2p orbitals on carbon. The localized sp3 orbitals corresponding to each individual bond in valence bond theory can be obtained from a combination of the four molecular orbitals
13.
Temperature
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A temperature is an objective comparative measurement of hot or cold. It is measured by a thermometer, several scales and units exist for measuring temperature, the most common being Celsius, Fahrenheit, and, especially in science, Kelvin. Absolute zero is denoted as 0 K on the Kelvin scale, −273.15 °C on the Celsius scale, the kinetic theory offers a valuable but limited account of the behavior of the materials of macroscopic bodies, especially of fluids. Temperature is important in all fields of science including physics, geology, chemistry, atmospheric sciences, medicine. The Celsius scale is used for temperature measurements in most of the world. Because of the 100 degree interval, it is called a centigrade scale.15, the United States commonly uses the Fahrenheit scale, on which water freezes at 32°F and boils at 212°F at sea-level atmospheric pressure. Many scientific measurements use the Kelvin temperature scale, named in honor of the Scottish physicist who first defined it and it is a thermodynamic or absolute temperature scale. Its zero point, 0K, is defined to coincide with the coldest physically-possible temperature and its degrees are defined through thermodynamics. The temperature of zero occurs at 0K = −273. 15°C. For historical reasons, the triple point temperature of water is fixed at 273.16 units of the measurement increment, Temperature is one of the principal quantities in the study of thermodynamics. There is a variety of kinds of temperature scale and it may be convenient to classify them as empirically and theoretically based. Empirical temperature scales are historically older, while theoretically based scales arose in the middle of the nineteenth century, empirically based temperature scales rely directly on measurements of simple physical properties of materials. For example, the length of a column of mercury, confined in a capillary tube, is dependent largely on temperature. Such scales are only within convenient ranges of temperature. For example, above the point of mercury, a mercury-in-glass thermometer is impracticable. A material is of no use as a thermometer near one of its phase-change temperatures, in spite of these restrictions, most generally used practical thermometers are of the empirically based kind. Especially, it was used for calorimetry, which contributed greatly to the discovery of thermodynamics, nevertheless, empirical thermometry has serious drawbacks when judged as a basis for theoretical physics. Theoretically based temperature scales are based directly on theoretical arguments, especially those of thermodynamics, kinetic theory and they rely on theoretical properties of idealized devices and materials
14.
Electric potential
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An electric potential is the amount of work needed to move a unit positive charge from a reference point to a specific point inside the field without producing any acceleration. Typically, the point is Earth or a point at Infinity. By dividing out the charge on the particle a remainder is obtained that is a property of the field itself. This value can be calculated in either a static or an electric field at a specific time in units of joules per coulomb. The electric potential at infinity is assumed to be zero, a generalized electric scalar potential is also used in electrodynamics when time-varying electromagnetic fields are present, but this can not be so simply calculated. The electric potential and the vector potential together form a four vector. Classical mechanics explores concepts such as force, energy, potential etc, force and potential energy are directly related. A net force acting on any object will cause it to accelerate, as it rolls downhill its potential energy decreases, being translated to motion, inertial energy. It is possible to define the potential of certain force fields so that the energy of an object in that field depends only on the position of the object with respect to the field. Two such force fields are the field and an electric field. Such fields must affect objects due to the properties of the object. Objects may possess a property known as charge and an electric field exerts a force on charged objects. If the charged object has a charge the force will be in the direction of the electric field vector at that point while if the charge is negative the force will be in the opposite direction. The magnitude of the force is given by the quantity of the charge multiplied by the magnitude of the field vector. The electric potential at a point r in an electric field E is given by the line integral where C is an arbitrary path connecting the point with zero potential to r. When the curl ∇ × E is zero, the integral above does not depend on the specific path C chosen. The concept of electric potential is linked with potential energy. A test charge q has a potential energy UE given by U E = q V
15.
Sensor
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A sensor is always used with other electronics, whether as simple as a light or as complex as a computer. Moreover, analog sensors such as potentiometers and force-sensing resistors are still widely used, applications include manufacturing and machinery, airplanes and aerospace, cars, medicine, robotics and many other aspects of our day-to-day life. A sensors sensitivity indicates how much the output changes when the input quantity being measured changes. For instance, if the mercury in a thermometer moves 1 cm when the changes by 1 °C. Some sensors can also affect what they measure, for instance, Sensors are usually designed to have a small effect on what is measured, making the sensor smaller often improves this and may introduce other advantages. Technological progress allows more and more sensors to be manufactured on a scale as microsensors using MEMS technology. In most cases, a microsensor reaches a higher speed. Most sensors have a transfer function. The sensitivity is defined as the ratio between the output signal and measured property. For example, if a sensor measures temperature and has a voltage output, the sensitivity is the slope of the transfer function. Converting the sensors electrical output to the measured units requires dividing the output by the slope. In addition, an offset is added or subtracted. For example -40 must be added to the output if 0 V output corresponds to -40 C input, for an analog sensor signal to be processed, or used in digital equipment, it needs to be converted to a digital signal, using an analog-to-digital converter. The full scale range defines the maximum and minimum values of the measured property, the sensitivity may in practice differ from the value specified. This is called a sensitivity error and this is an error in the slope of a linear transfer function. If the output differs from the correct value by a constant. This is an error in the y-intercept of a transfer function. Nonlinearity is deviation of a transfer function from a straight line transfer function
16.
Review
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In addition to a critical evaluation, the reviews author may assign the work a rating to indicate its relative merit. More loosely, an author may review current events, trends, a compilation of reviews may itself be called a review. The New York Review of Books, for instance, is a collection of essays on literature, culture, national Review, founded by William F. Buckley, Jr. is an influential conservative magazine, and Monthly Review is a long-running socialist periodical. A peer review is the process by which scholars or scientists assess the work of their colleagues that has been submitted for publication in the scientific or scholarly literature. In the scientific literature, review articles are a category of scientific or scholarly paper, a compilation of these reviews forms the core content of review journals. Beyond review articles in journals, a review may be found in an encyclopedia or a critical book review. In computer programming and the development process, a software review may be used. A user review refers to a written by a user or consumer for a product or a service based on her experience as a user of the reviewed product. Popular sources for consumer reviews are e-commerce sites like Amazon or Zappos, e-commerce sites often have consumer reviews for products and sellers separately. Usually, consumer reviews are in the form of lines of texts accompanied by a numerical rating. This text is meant to aid in shopping decision of a prospective buyer, a consumer review of a product usually comments on how well the product measures up to expectations based on the specifications provided by the manufacturer or seller. It talks about performance, reliability, quality defects, if any, consumer review, also called word of mouth and user generated content differs from marketer generated content in its evaluation from consumer or user point of view. Often it includes comparative evaluations against competing products, observations are factual as well as subjective in nature. Consumer review of sellers usually comment on service experienced, and dependability or trustworthiness of the seller, usually, it comments on factors such as timeliness of delivery, packaging, and correctness of delivered items, shipping charges, return services against promises made, and so on. Consumer reviews online have become a factor in business reputation and brand image due to the popularity of TripAdvisor, Yelp. An expert review usually refers to a written by someone who has tested several peer products or services to identify which offers the best value for money or the best set of features. A bought review is the system where the creator of a new product pays a reviewer to review his new product, a is a form of criticism in which a book is analyzed based on content, style, and merit. It is often carried out in periodicals, as school work and its length may vary from a single paragraph to a substantial
17.
Bipolaron
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In physics, a bipolaron is a type of quasiparticle consisting of two polarons. In organic chemistry, it is a molecule or a part of a chain containing two positive charges in a conjugated system. In physics, a bipolaron is a pair of two polarons. An electron in a material may cause a distortion in the underlying lattice, the combination of electron and distortion is known as a polaron. When two polarons are close together, they can lower their energy by sharing the same distortions, if the interaction is sufficiently large, then that attraction leads to a bound bipolaron. For strong attraction, bipolarons may be small, small bipolarons have integer spin and thus share some of the properties of bosons. If many bipolarons form without coming too close, they might be able to form a Bose–Einstein condensate and this has led to a suggestion that bipolarons could be a possible mechanism for high-temperature superconductivity. For example, they can lead to a direct interpretation of the isotope effect. In organic chemistry, a bipolaron is a molecule or part of a chain containing two positive charges in a conjugated system. The charges can be located in the centre of the chain or at its termini, bipolarons and polarons are encountered in doped conducting polymers such as polythiophene. It is possible to synthesize and isolate bipolaron model compounds for X-ray diffraction studies, the diamagnetic bisamine dication 2 in scheme 1 is prepared from the neutral precursor 1 in dichloromethane by reaction with 4 equivalents of antimony pentachloride. Two resonance structures exist for the dication, structure 2a is a diradical and 2b is the closed shell quinoid. The experimental bond lengths for the central group in 2 are 141 pm and 137 pm compared to 144 pm and 134 pm for the precursor 1 implying some contribution from the quinoid structure. On the other hand, when a unit is added to the core in the structure depicted in scheme 2
18.
Iodine
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Iodine is a chemical element with symbol I and atomic number 53. The heaviest of the halogens, it exists as a lustrous. The elemental form was discovered by the French chemist Bernard Courtois in 1811 and it was named two years later by Joseph-Louis Gay-Lussac from this property, after the Greek ἰωδης violet-coloured. Iodine occurs in many states, including iodide, iodate. It is the least abundant of the halogens, being the sixty-first most abundant element. It is even less abundant than the rare earths. It is the heaviest essential element, iodine is found in the thyroid hormones. Iodine deficiency affects two billion people and is the leading preventable cause of intellectual disabilities. The dominant producers of today are Chile and Japan. Iodine and its compounds are used in nutrition. Due to its atomic number and ease of attachment to organic compounds. Because of the specificity of its uptake by the human body, iodine is also used as a catalyst in the industrial production of acetic acid and some polymers. In 1811, iodine was discovered by French chemist Bernard Courtois, at that time of the Napoleonic Wars, saltpeter was in great demand in France. Saltpeter produced from French nitre beds required sodium carbonate, which could be isolated from seaweed collected on the coasts of Normandy, to isolate the sodium carbonate, seaweed was burned and the ash washed with water. The remaining waste was destroyed by adding sulfuric acid, Courtois once added excessive sulfuric acid and a cloud of purple vapour rose. He noted that the vapour crystallised on cold surfaces, making dark crystals, Courtois suspected that this material was a new element but lacked funding to pursue it further. Courtois gave samples to his friends, Charles Bernard Desormes and Nicolas Clément and he also gave some of the substance to chemist Joseph Louis Gay-Lussac, and to physicist André-Marie Ampère. On 29 November 1813, Desormes and Clément made Courtois discovery public and they described the substance to a meeting of the Imperial Institute of France
19.
Copper
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Copper is a chemical element with symbol Cu and atomic number 29. It is a soft, malleable, and ductile metal with high thermal and electrical conductivity. A freshly exposed surface of copper has a reddish-orange color. Copper is one of the few metals that occur in nature in directly usable metallic form as opposed to needing extraction from an ore and this led to very early human use, from c.8000 BC. Copper used in buildings, usually for roofing, oxidizes to form a green verdigris, Copper is sometimes used in decorative art, both in its elemental metal form and in compounds as pigments. Copper compounds are used as agents, fungicides, and wood preservatives. Copper is essential to all living organisms as a trace dietary mineral because it is a key constituent of the enzyme complex cytochrome c oxidase. In molluscs and crustaceans, copper is a constituent of the blood pigment hemocyanin, replaced by the hemoglobin in fish. In humans, copper is found mainly in the liver, muscle, the adult body contains between 1.4 and 2.1 mg of copper per kilogram of body weight. The filled d-shells in these elements contribute little to interatomic interactions, unlike metals with incomplete d-shells, metallic bonds in copper are lacking a covalent character and are relatively weak. This observation explains the low hardness and high ductility of single crystals of copper, at the macroscopic scale, introduction of extended defects to the crystal lattice, such as grain boundaries, hinders flow of the material under applied stress, thereby increasing its hardness. For this reason, copper is supplied in a fine-grained polycrystalline form. The softness of copper partly explains its high conductivity and high thermal conductivity. The maximum permissible current density of copper in open air is approximately 3. 1×106 A/m2 of cross-sectional area, Copper is one of a few metallic elements with a natural color other than gray or silver. Pure copper is orange-red and acquires a reddish tarnish when exposed to air, as with other metals, if copper is put in contact with another metal, galvanic corrosion will occur. A green layer of verdigris can often be seen on old structures, such as the roofing of many older buildings. Copper tarnishes when exposed to sulfur compounds, with which it reacts to form various copper sulfides. There are 29 isotopes of copper, 63Cu and 65Cu are stable, with 63Cu comprising approximately 69% of naturally occurring copper, both have a spin of 3⁄2
20.
Polythiophene
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Polythiophenes are polymerized thiophenes, a sulfur heterocycle. They can become conducting when oxidized, the most notable property of these materials, electrical conductivity, results from the delocalization of electrons along the polymer backbone – hence the term synthetic metals. Conductivity however is not the only interesting property resulting from electron delocalization, a number of comprehensive reviews have been published on PTs, the earliest dating from 1981. Schopf and Koßmehl published a review of the literature published between 1990 and 1994. Roncali surveyed electrochemical synthesis in 1992, and the properties of substituted PTs in 1997. McCulloughs 1998 review focussed on chemical synthesis of conducting PTs, a general review of conjugated polymers from the 1990s was conducted by Reddinger and Reynolds in 1999. Finally, Swager et al. examined conjugated-polymer-based chemical sensors in 2000 and these reviews are an excellent guide to the highlights of the primary PT literature from the last two decades. Electrons are delocalized along the conjugated backbones of conducting polymers, usually through overlap of π-orbitals, by removing electrons from the π-system, or adding electrons into the π-system, a charged unit called a bipolaron is formed. Doping is performed at higher levels in conducting polymers than in semiconductors. The bipolaron moves as a unit along the chain, and is responsible for the macroscopically observed conductivity of the polymer. For some samples of poly doped with iodine, the conductivity can approach 1000 S/cm, generally, the conductivity of PTs is lower than 1000 S/cm, but high conductivity is not necessary for many applications of conducting polymers. Simultaneous oxidation of the polymer and introduction of counterions, p-doping. During the electrochemical synthesis of a PT, counterions dissolved in the solvent can associate with the polymer as it is deposited onto the electrode in its oxidized form. By doping the polymer as it is synthesized, a film can build up on an electrode—the polymer conducts electrons from the substrate to the surface of the film. Alternatively, a conducting polymer film or solution can be doped post-synthesis. Reduction of the polymer, n-doping, is much less common than p-doping. A variety of reagents have been used to dope PTs, iodine and bromine produce highly conductive materials, which are unstable owing to slow evaporation of the halogen. Organic acids, including trifluoroacetic acid, propionic acid, and sulfonic acids produce PTs with lower conductivities than iodine, poly dissolved in toluene can be doped by solutions of ferric chloride hexahydrate dissolved in acetonitrile, and can be cast into films with conductivities reaching 1 S/cm
21.
Electrochemistry
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These reactions involve electric charges moving between electrodes and an electrolyte. Thus electrochemistry deals with the interaction between electrical energy and chemical change, chemical reactions where electrons are transferred directly between molecules and/or atoms are called oxidation-reduction or reactions. In general, electrochemistry describes the reactions when individual redox reactions are separate but connected by an external electric circuit. Understanding of electrical matters began in the sixteenth century, during this century, the English scientist William Gilbert spent 17 years experimenting with magnetism and, to a lesser extent, electricity. For his work on magnets, Gilbert became known as the Father of Magnetism and he discovered various methods for producing and strengthening magnets. In 1663, the German physicist Otto von Guericke created the first electric generator, the generator was made of a large sulfur ball cast inside a glass globe, mounted on a shaft. The ball was rotated by means of a crank and a spark was produced when a pad was rubbed against the ball as it rotated. The globe could be removed and used as source for experiments with electricity, by the mid—18th century the French chemist Charles François de Cisternay du Fay had discovered two types of static electricity, and that like charges repel each other whilst unlike charges attract. Du Fay announced that electricity consisted of two fluids, vitreous, or positive, electricity, and resinous, or negative, electricity and this was the two-fluid theory of electricity, which was to be opposed by Benjamin Franklins one-fluid theory later in the century. Galvani refuted this by obtaining muscular action with two pieces of the same material, in 1800, William Nicholson and Johann Wilhelm Ritter succeeded in decomposing water into hydrogen and oxygen by electrolysis. Soon thereafter Ritter discovered the process of electroplating and he also observed that the amount of metal deposited and the amount of oxygen produced during an electrolytic process depended on the distance between the electrodes. By 1801, Ritter observed thermoelectric currents and anticipated the discovery of thermoelectricity by Thomas Johann Seebeck, by the 1810s, William Hyde Wollaston made improvements to the galvanic cell. This work led directly to the isolation of sodium and potassium from their compounds, andré-Marie Ampère quickly repeated Ørsteds experiment, and formulated them mathematically. In 1821, Estonian-German physicist Thomas Johann Seebeck demonstrated the potential in the juncture points of two dissimilar metals when there is a heat difference between the joints. In 1827, the German scientist Georg Ohm expressed his law in this famous book Die galvanische Kette, in 1832, Michael Faradays experiments led him to state his two laws of electrochemistry. In 1836, John Daniell invented a primary cell which solved the problem of polarization by eliminating hydrogen gas generation at the positive electrode, later results revealed that alloying the amalgamated zinc with mercury would produce a higher voltage. William Grove produced the first fuel cell in 1839, in 1846, Wilhelm Weber developed the electrodynamometer. In 1868, Georges Leclanché patented a new cell which became the forerunner to the worlds first widely used battery
22.
Chemistry
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Chemistry is a branch of physical science that studies the composition, structure, properties and change of matter. Chemistry is sometimes called the science because it bridges other natural sciences, including physics. For the differences between chemistry and physics see comparison of chemistry and physics, the history of chemistry can be traced to alchemy, which had been practiced for several millennia in various parts of the world. The word chemistry comes from alchemy, which referred to a set of practices that encompassed elements of chemistry, metallurgy, philosophy, astrology, astronomy, mysticism. An alchemist was called a chemist in popular speech, and later the suffix -ry was added to this to describe the art of the chemist as chemistry, the modern word alchemy in turn is derived from the Arabic word al-kīmīā. In origin, the term is borrowed from the Greek χημία or χημεία and this may have Egyptian origins since al-kīmīā is derived from the Greek χημία, which is in turn derived from the word Chemi or Kimi, which is the ancient name of Egypt in Egyptian. Alternately, al-kīmīā may derive from χημεία, meaning cast together, in retrospect, the definition of chemistry has changed over time, as new discoveries and theories add to the functionality of the science. The term chymistry, in the view of noted scientist Robert Boyle in 1661, in 1837, Jean-Baptiste Dumas considered the word chemistry to refer to the science concerned with the laws and effects of molecular forces. More recently, in 1998, Professor Raymond Chang broadened the definition of chemistry to mean the study of matter, early civilizations, such as the Egyptians Babylonians, Indians amassed practical knowledge concerning the arts of metallurgy, pottery and dyes, but didnt develop a systematic theory. Greek atomism dates back to 440 BC, arising in works by such as Democritus and Epicurus. In 50 BC, the Roman philosopher Lucretius expanded upon the theory in his book De rerum natura, unlike modern concepts of science, Greek atomism was purely philosophical in nature, with little concern for empirical observations and no concern for chemical experiments. Work, particularly the development of distillation, continued in the early Byzantine period with the most famous practitioner being the 4th century Greek-Egyptian Zosimos of Panopolis. He formulated Boyles law, rejected the four elements and proposed a mechanistic alternative of atoms. Before his work, though, many important discoveries had been made, the Scottish chemist Joseph Black and the Dutchman J. B. English scientist John Dalton proposed the theory of atoms, that all substances are composed of indivisible atoms of matter. Davy discovered nine new elements including the alkali metals by extracting them from their oxides with electric current, british William Prout first proposed ordering all the elements by their atomic weight as all atoms had a weight that was an exact multiple of the atomic weight of hydrogen. The inert gases, later called the noble gases were discovered by William Ramsay in collaboration with Lord Rayleigh at the end of the century, thereby filling in the basic structure of the table. Organic chemistry was developed by Justus von Liebig and others, following Friedrich Wöhlers synthesis of urea which proved that organisms were, in theory
23.
Bromine
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Bromine is a chemical element with symbol Br and atomic number 35. It is the third-lightest halogen, and is a fuming red-brown liquid at room temperature that readily to form a similarly coloured gas. Its properties are intermediate between those of chlorine and iodine. Isolated independently by two chemists, Carl Jacob Löwig and Antoine Jérôme Balard, its name was derived from the Ancient Greek βρῶμος stench, referencing its sharp and disagreeable smell. Elemental bromine is very reactive and thus does not occur free in nature, while it is rather rare in the Earths crust, the high solubility of the bromide ion has caused its accumulation in the oceans. Commercially the element is easily extracted from brine pools, mostly in the United States, Israel, the mass of bromine in the oceans is about one three-hundredth of that of chlorine. At high temperatures, organobromine compounds readily convert to free bromine atoms and this effect makes organobromine compounds useful as fire retardants and more than half the bromine produced worldwide each year is put to this purpose. Unfortunately, the same property causes sunlight to convert volatile organobromine compounds to free bromine atoms in the atmosphere, as a result, many organobromide compounds—such as the pesticide methyl bromide—are no longer used. Bromine compounds are used in well drilling fluids, in photographic film. Bromine has sometimes been considered to be essential in humans, but with the support of only limited circumstantial evidence. As a pharmaceutical, the bromide ion has inhibitory effects on the central nervous system. They retain niche uses as antiepileptics, bromine was discovered independently by two chemists, Carl Jacob Löwig and Antoine Balard, in 1825 and 1826, respectively. Löwig isolated bromine from a water spring from his hometown Bad Kreuznach in 1825. Löwig used a solution of the mineral salt saturated with chlorine, after evaporation of the ether a brown liquid remained. With this liquid as a sample for his work he applied for a position in the laboratory of Leopold Gmelin in Heidelberg, the publication of the results was delayed and Balard published his results first. Balard found bromine chemicals in the ash of seaweed from the marshes of Montpellier. The seaweed was used to produce iodine, but also contained bromine, Balard distilled the bromine from a solution of seaweed ash saturated with chlorine. In his publication, Balard states that he changed the name from muride to brôme on the proposal of M. Anglada, brôme derives from the Greek βρωμος
24.
Organic acid
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An organic acid is an organic compound with acidic properties. The most common organic acids are the carboxylic acids, whose acidity is associated with their carboxyl group –COOH, sulfonic acids, containing the group –SO2OH, are relatively stronger acids. Alcohols, with –OH, can act as acids but they are very weak. The relative stability of the base of the acid determines its acidity. Other groups can also confer acidity, usually weakly, the thiol group –SH, the group. In biological systems, organic compounds containing these groups are referred to as organic acids. In general, organic acids are acids and do not dissociate completely in water. Lower molecular mass organic acids such as formic and lactic acids are miscible in water, on the other hand, most organic acids are very soluble in organic solvents. P-Toluenesulfonic acid is a strong acid used in organic chemistry often because it is able to dissolve in the organic reaction solvent. Exceptions to these solubility characteristics exist in the presence of other substituents that affect the polarity of the compound. The pKa a logarithmic measure of the dissociation constant, categorizes the strength of an acid, the lower or more negative the number. It should not be confused with pH, the measure of actual hydrogen ion concentration. Phenol C6H5OH The 19th century name carbolic acid came from the original German name karbolsäure and it is a weak, non-carboxylic acid, but is corrosive and causes chemical burns on the skin due to a protein-degenerating effect. Uric acid C5H4N4O3 Uric acid is a purine derivative which is a diprotic acid but not a carboxylic one. Taurine C2H7NO3S One of the few natural sulfonic acids, discovered in bile, p-Toluenesulfonic acid CH3C6H4SO3H A strong acid that, unlike some strong mineral acids, is non-oxidizing. Trifluoromethanesulfonic acid CF3SO3H One of the strongest acids in existence, organic or inorganic, about a thousand times stronger than sulfuric acid, first synthesized in 1954, it also resists oxidation/reduction reactions and does not sulfonate substrates like sulfuric or chlorosulfonic acid. Aminomethylphosphonic acid A strong phosphonic acid Simple organic acids like formic or acetic acids are used for oil and these organic acids are much less reactive with metals than are strong mineral acids like hydrochloric acid or mixtures of HCl and hydrofluoric acid. For this reason, organic acids are used at temperatures or when long contact times between acid and pipe are needed
25.
Trifluoroacetic acid
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Trifluoroacetic acid is an organofluorine compound with the chemical formula CF3CO2H. It is a liquid with a sharp odor similar to vinegar. TFA is an analogue of acetic acid with the three hydrogen atoms replaced by three fluorine atoms, the acidity of TFA is approximately 34,000 times stronger than that of acetic acid due to the electronegativity of the trifluoromethyl group. TFA is widely used in chemistry for various purposes. An older route to TFA proceeds via the oxidation of 1,1, 1-trifluoro-2,3, the trifluorotrichloropropene can be prepared by Swarts fluorination of hexachloropropene. TFA occurs naturally in sea water, but only in small concentrations, TFA is the precursor to many other fluorinated compounds such as trifluoroacetic anhydride, trifluoroperacetic acid, and 2,2, 2-trifluoroethanol. It is a reagent used in organic synthesis because of a combination of convenient properties, volatility, solubility in organic solvents, TFA is also less oxidizing than sulfuric acid but more readily available in anhydrous form than many other acids. One complication to its use is that TFA forms an azeotrope with water, TFA is popularly used as a strong acid in peptide synthesis and other organic synthesis to remove the t-butoxycarbonyl protecting group. At a low concentration, TFA is used as an ion pairing agent in liquid chromatography of organic compounds, particularly peptides, TFA is a versatile solvent for NMR spectroscopy. It is also used as a calibrant in mass spectrometry, TFA is used to produce trifluoroacetate salts. Trifluoroacetic acid is a corrosive acid but it does not pose the hazards associated with hydrofluoric acid because the bond is not labile. Only if heated or treated with ultrasonic waves will it decompose into hydrofluoric acid, TFA is harmful when inhaled, causes severe skin burns and is toxic for water organisms even at low concentrations. TFAs reaction with bases and metals, especially metals, is strongly exothermic. The reaction with lithium aluminium hydride results in an explosion, TFA is neither readily nor inherently biodegradable although it does not readily bioaccumulate. In water, it is toxic to algae, fluoroacetic acid Difluoroacetic acid Trichloroacetic acid, the chlorinated analog
26.
Propionic acid
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Propionic acid is a naturally occurring carboxylic acid with chemical formula CH3CH2COOH. It is a liquid with a pungent and unpleasant smell somewhat resembling body odor. The anion CH3CH2COO− as well as the salts and esters of propionic acid are known as propionates, Propionic acid was first described in 1844 by Johann Gottlieb, who found it among the degradation products of sugar. Over the next few years, other chemists produced propionic acid in various other ways, Propionic acid has physical properties intermediate between those of the smaller carboxylic acids, formic and acetic acids, and the larger fatty acids. It is miscible with water, but can be removed from water by adding salt, as with acetic and formic acids, it consists of hydrogen bonded pairs of molecules as both the liquid and the vapor. Propionic acid displays the properties of carboxylic acids, It can form amide, ester, anhydride. It can undergo alpha-halogenation with bromine in the presence of PBr3 as catalyst to form CH3CHBrCOOH, in the presence of cobalt or manganese ions, this reaction proceeds rapidly at temperatures as mild as 40–50 °C, CH3CH2CHO + 1⁄2 O2 → CH3CH2COOH. Large amounts of propionic acid were produced as a byproduct of acetic acid manufacture. At the current time, the worlds largest producer of propionic acid is BASF, bacteria of the genus Propionibacterium produce propionic acid as the end-product of their anaerobic metabolism. This class of bacteria is found in the stomachs of ruminants and the sweat glands of humans. It is also biosynthesized in the intestine of humans by bacterial fermentation of dietary fibre. Propionic acid inhibits the growth of mold and some bacteria at the levels between 0.1 and 1% by weight, as a result, most propionic acid produced is consumed as a preservative for both animal feed and food for human consumption. For animal feed, it is used directly or as its ammonium salt. The antibiotic Monensin is added to feed to favor propionibacteria over acetic acid producers in the rumen. This application accounts for half of the world production of propionic acid. Another major application is as a preservative in baked goods, which use the sodium and calcium salts, as a food additive, it is approved for use in the EU, USA and Australia and New Zealand. It is listed by its INS number or E number E280, Propionic acid is also useful as an intermediate in the production of other chemicals, especially polymers. In more specialized applications, it is used to make pesticides
27.
Sulfonic acid
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A sulfonic acid refers to a member of the class of organosulfur compounds with the general formula R−S2−OH, where R is an organic alkyl or aryl group and the S2−OH group a sulfonyl hydroxide. A sulfonic acid can be thought of as sulfuric acid with one hydroxyl group replaced by an organic substituent, the parent compound is the hypothetical compound sulfurous acid. Salts or esters of sulfonic acids are called sulfonates, a sulfonic acid is produced by the process of sulfonation. Usually the sulfonating agent is sulfur trioxide, thiols can be oxidized to sulfonic acids, RSH + 3⁄2 O2 → RSO3H Certain sulfonic acids, such as perfluorooctanesulfonic acid, are prepared by electrophilic fluorination of preformed sulfonic acids. The net conversion can be represented simplistically, C8H17SO3H +17 F2 → C8F17SO3H +17 HF Sulfonic acids are much stronger acids than the carboxylic acids. P-Toluenesulfonic acid, with a pKa of −2.8, is about a million times stronger acid than benzoic acid, similarly, methanesulfonic acid, pKa = −1.9, is also about one million times stronger acid than acetic acid. Because of their polarity, sulfonic acids tend to be crystalline solids and they are also usually colourless and nonoxidizing, which is convenient. Because of their acidity, sulfonic acids are often soluble in water or exhibit detergent-like properties. The structure of sulfonic acids is illustrated by the prototype, methanesulfonic acid, the sulfonic acid group, RSO2OH features a tetrahedral sulfur centre, meaning that sulfur is at the center of four atoms, three oxygens and one carbon. The overall geometry of the centre is reminiscent of the shape of sulfuric acid. Although both alkyl and aryl sulfonic acids are known, most of the applications are associated with the aromatic derivatives, detergents and surfactants are molecules that combine highly nonpolar and highly polar groups. Traditionally, soaps are the popular surfactants, being derived from fatty acids, since the mid-20th century, the usage of sulfonic acids has surpassed soap in advanced societies. For example, an estimated 2 billion kilograms of alkylbenzenesulfonates are produced annually for diverse purposes, lignin sulfonates, produced by sulfonation of lignin are components of drilling fluids and additives in certain kinds of concrete. Many if not most of the dyes are produced or processed via sulfonation. Sulfonic acids tend to tightly to proteins and carbohydrates. Most washable dyes are sulfonic acids for this reason, p-Cresidinesulfonic acid is used to make food dyes. Being strong acids, sulfonic acids are used as catalysts. The simplest examples are methanesulfonic acid, CH3SO2OH and p-toluenesulfonic acid, polymeric sulfonic acids are also useful
28.
Iron(III) chloride
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Iron chloride, also called ferric chloride, is an industrial scale commodity chemical compound, with the formula FeCl3 and with iron in the +3 oxidation state. The colour of iron chloride crystals depends on the angle, by reflected light the crystals appear dark green. Anhydrous iron chloride is deliquescent, forming hydrated hydrogen chloride mists in moist air and it is rarely observed in its natural form, the mineral molysite, known mainly from some fumaroles. When dissolved in water, iron chloride undergoes hydrolysis and gives off heat in an exothermic reaction, the resulting brown, acidic, and corrosive solution is used as a flocculant in sewage treatment and drinking water production, and as an etchant for copper-based metals in printed circuit boards. Anhydrous iron chloride is a fairly strong Lewis acid, and it is used as a catalyst in organic synthesis, the descriptor hydrated or anhydrous is used when referring to iron chloride, to distinguish between the two common forms. The hexahydrate is usually given as the empirical formula FeCl3⋅6H2O. It may also be given as trans-Cl⋅2H2O and the systematic name tetraaquadichloroiron chloride dihydrate, anhydrous iron chloride adopts the BiI3 structure, which features octahedral Fe centres interconnected by two-coordinate chloride ligands. Iron chloride hexahydrate consists of trans-+ cationic complexes and chloride anions, Iron chloride has a relatively low melting point and boils at around 315 °C. Anhydrous iron chloride may be prepared by union of the elements,2 Fe +3 Cl2 →2 FeCl3 Solutions of iron chloride are produced both from iron and from ore, in a closed-loop process. Conversion of the hydrate to anhydrous iron chloride is not accomplished by heating, as HCl, Iron chloride undergoes hydrolysis to give an acidic solution. When heated with iron oxide at 350 °C, iron chloride gives iron oxychloride, FeCl3 + Fe2O3 →3 FeOCl It is a moderately strong Lewis acid, forming adducts with Lewis bases such as triphenylphosphine oxide, e. g. FeCl32 where Ph = phenyl. It also reacts with other salts to give the yellow tetrahedral FeCl4− ion. Salts of FeCl4− in hydrochloric acid can be extracted into diethyl ether, alkali metal alkoxides react to give the metal alkoxide complexes of varying complexity. The compounds can be dimeric or trimeric, other carboxylate salts form complexes, e. g. citrate and tartrate. Iron chloride is a mild oxidising agent, for example, it is capable of oxidising copper chloride to copper chloride. FeCl3 + CuCl → FeCl2 + CuCl2 It also reacts with iron to iron chloride,2 FeCl3 + Fe →3 FeCl2 Reducing agents such as hydrazine convert iron chloride to complexes of iron. Iron chloride is used in treatment and drinking water production. In this application, FeCl3 in slightly basic water reacts with the ion to form a floc of iron hydroxide, or more precisely formulated as FeO−
29.
Catalysis
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Catalysis is the increase in the rate of a chemical reaction due to the participation of an additional substance called a catalyst. In most cases, reactions occur faster with a catalyst because they require less activation energy, furthermore, since they are not consumed in the catalyzed reaction, catalysts can continue to act repeatedly. Often only tiny amounts are required in principle, in the presence of a catalyst, less free energy is required to reach the transition state, but the total free energy from reactants to products does not change. A catalyst may participate in multiple chemical transformations, the effect of a catalyst may vary due to the presence of other substances known as inhibitors or poisons or promoters. Catalyzed reactions have an activation energy than the corresponding uncatalyzed reaction, resulting in a higher reaction rate at the same temperature. However, the mechanics of catalysis is complex. Usually, the catalyst participates in this slowest step, and rates are limited by amount of catalyst, in heterogeneous catalysis, the diffusion of reagents to the surface and diffusion of products from the surface can be rate determining. A nanomaterial-based catalyst is an example of a heterogeneous catalyst, analogous events associated with substrate binding and product dissociation apply to homogeneous catalysts. Although catalysts are not consumed by the reaction itself, they may be inhibited, deactivated, in heterogeneous catalysis, typical secondary processes include coking where the catalyst becomes covered by polymeric side products. Additionally, heterogeneous catalysts can dissolve into the solution in a system or sublimate in a solid–gas system. The production of most industrially important chemicals involves catalysis, similarly, most biochemically significant processes are catalysed. Research into catalysis is a field in applied science and involves many areas of chemistry, notably organometallic chemistry. Catalysis is relevant to aspects of environmental science, e. g. the catalytic converter in automobiles. Many transition metals and transition metal complexes are used in catalysis as well, Catalysts called enzymes are important in biology. A catalyst works by providing a reaction pathway to the reaction product. The rate of the reaction is increased as this route has a lower activation energy than the reaction route not mediated by the catalyst. The disproportionation of hydrogen peroxide creates water and oxygen, as shown below,2 H2O2 →2 H2O + O2 This reaction is preferable in the sense that the reaction products are more stable than the starting material, though the uncatalysed reaction is slow. In fact, the decomposition of hydrogen peroxide is so slow that hydrogen peroxide solutions are commercially available and this reaction is strongly affected by catalysts such as manganese dioxide, or the enzyme peroxidase in organisms
30.
Matrix-assisted laser desorption/ionization
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In mass spectrometry, matrix-assisted laser desorption/ionization is a ionization technique that uses a laser energy absorbing matrix to create [s from large molecules with minimal fragmentation. It has been applied to the analysis of biomolecules and large organic molecules, MALDI methodology is a three-step process. First, the sample is mixed with a matrix material. Second, a pulsed laser irradiates the sample, triggering ablation and desorption of the sample, finally, the analyte molecules are ionized by being protonated or deprotonated in the hot plume of ablated gases, and can then be accelerated into whichever mass spectrometer is used to analyse them. The term matrix-assisted laser desorption ionization was coined in 1985 by Franz Hillenkamp, Michael Karas and these researchers found that the amino acid alanine could be ionized more easily if it was mixed with the amino acid tryptophan and irradiated with a pulsed 266 nm laser. The tryptophan was absorbing the energy and helping to ionize the non-absorbing alanine. Peptides up to the 2843 Da peptide melittin could be ionized when mixed with this kind of “matrix”, Karas and Hillenkamp were subsequently able to ionize the 67 kDa protein albumin using a nicotinic acid matrix and a 266 nm laser. Further improvements were realized through the use of a 355 nm laser, today, mostly organic matrices are used for MALDI mass spectrometry. The matrix consists of crystallized molecules, of which the three most commonly used are 3, 5-dimethoxy-4-hydroxycinnamic acid, α-cyano-4-hydroxycinnamic acid and 2, 5-dihydroxybenzoic acid. A solution of one of these molecules is made, often in a mixture of highly purified water, a counter ion source such as Trifluoroacetic acid is usually added to generate the ions. A good example of a matrix-solution would be 20 mg/mL sinapinic acid in ACN, water, the identification of suitable matrix compounds is determined to some extent by trial and error, but they are based on some specific molecular design considerations. They are of a low molecular weight, but are large enough not to evaporate during sample preparation or while standing in the mass spectrometer. They are often acidic, therefore act as a source to encourage ionization of the analyte. Basic matrices have also been reported and they have a strong optical absorption in either the UV or IR range, so that they rapidly and efficiently absorb the laser irradiation. This efficiency is commonly associated with chemical structures incorporating several conjugated double bonds and they are functionalized with polar groups, allowing their use in aqueous solutions. The matrix solution is mixed with the analyte, a mixture of water and organic solvent allows both hydrophobic and water-soluble molecules to dissolve into the solution. This solution is spotted onto a MALDI plate, the solvents vaporize, leaving only the recrystallized matrix, but now with analyte molecules embedded into MALDI crystals. The matrix and the analyte are said to be co-crystallized, co-crystallization is a key issue in selecting a proper matrix to obtain a good quality mass spectrum of the analyte of interest
31.
Mass spectrometry
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Mass spectrometry is an analytical technique that ionizes chemical species and sorts the ions based on their mass-to-charge ratio. In simpler terms, a mass spectrum measures the masses within a sample, mass spectrometry is used in many different fields and is applied to pure samples as well as complex mixtures. A mass spectrum is a plot of the ion signal as a function of the mass-to-charge ratio, in a typical MS procedure, a sample, which may be solid, liquid, or gas, is ionized, for example by bombarding it with electrons. This may cause some of the molecules to break into charged fragments. The ions are detected by a capable of detecting charged particles. Results are displayed as spectra of the abundance of detected ions as a function of the mass-to-charge ratio. The atoms or molecules in the sample can be identified by correlating known masses to the masses or through a characteristic fragmentation pattern. Goldstein called these positively charged anode rays Kanalstrahlen, the translation of this term into English is canal rays. Wien found that the charge-to-mass ratio depended on the nature of the gas in the discharge tube, thomson later improved on the work of Wien by reducing the pressure to create the mass spectrograph. The word spectrograph had become part of the international scientific vocabulary by 1884, a mass spectroscope is similar to a mass spectrograph except that the beam of ions is directed onto a phosphor screen. A mass spectroscope configuration was used in early instruments when it was desired that the effects of adjustments be quickly observed, once the instrument was properly adjusted, a photographic plate was inserted and exposed. The term mass spectroscope continued to be used though the direct illumination of a phosphor screen was replaced by indirect measurements with an oscilloscope. The use of the mass spectroscopy is now discouraged due to the possibility of confusion with light spectroscopy. Mass spectrometry is often abbreviated as mass-spec or simply as MS, modern techniques of mass spectrometry were devised by Arthur Jeffrey Dempster and F. W. Aston in 1918 and 1919 respectively. Sector mass spectrometers known as calutrons were used for separating the isotopes of uranium developed by Ernest O. Lawrence during the Manhattan Project, calutron mass spectrometers were used for uranium enrichment at the Oak Ridge, Tennessee Y-12 plant established during World War II. In 1989, half of the Nobel Prize in Physics was awarded to Hans Dehmelt, a mass spectrometer consists of three components, an ion source, a mass analyzer, and a detector. The ionizer converts a portion of the sample into ions, there is a wide variety of ionization techniques, depending on the phase of the sample and the efficiency of various ionization mechanisms for the unknown species. An extraction system removes ions from the sample, which are then targeted through the mass analyzer, the differences in masses of the fragments allows the mass analyzer to sort the ions by their mass-to-charge ratio
32.
Toluene
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Toluene /ˈtɒljuːiːn/, also known as toluol /ˈtɒljuːɒl/, is a colorless, water-insoluble liquid with the smell associated with paint thinners. It is a benzene derivative, consisting of a CH3 group attached to a phenyl group. As such, its IUPAC systematic name is methylbenzene, Toluene is widely used as an industrial feedstock and a solvent. In 2013, worldwide sales of toluene amounted to about 24.5 billion US-dollars, as the solvent in some types of paint thinner, contact cement and model airplane glue, toluene is sometimes used as a recreational inhalant and has the potential of causing severe neurological harm. The compound was first isolated in 1837 through a distillation of oil by a Polish chemist named Filip Walter. In 1843, Jöns Jacob Berzelius recommended the name toluin, in 1850, French chemist Auguste Cahours isolated from a distillate of wood a hydrocarbon which he recognized as similar to Devilles benzoène and which Cahours named toluène. Toluene reacts as an aromatic hydrocarbon in electrophilic aromatic substitution. Because the methyl group has greater electron-releasing properties than an atom in the same position. It undergoes sulfonation to give p-toluenesulfonic acid, and chlorination by Cl2 in the presence of FeCl3 to give ortho, importantly, the methyl side chain in toluene is susceptible to oxidation. Toluene reacts with Potassium permanganate to yield benzoic acid, and with chromyl chloride to yield benzaldehyde, the methyl group undergoes halogenation under free radical conditions. For example, N-bromosuccinimide heated with toluene in the presence of AIBN leads to benzyl bromide, the same conversion can be effected with elemental bromine in the presence of UV light or even sunlight. Toluene may also be brominated by treating it with HBr and H2O2 in the presence of light. C6H5CH3 + Br2 → C6H5CH2Br + HBr C6H5CH2Br + Br2 → C6H5CHBr2 + HBr The methyl group in toluene undergoes deprotonation only with strong bases. Catalytic hydrogenation of toluene gives methylcyclohexane, the reaction requires a high pressure of hydrogen and a catalyst. Final separation and purification is done by any of the distillation or solvent extraction processes used for BTX aromatics, Toluene is so inexpensively produced industrially that it is not prepared in the laboratory. In principle it could be prepared by a variety of methods, Toluene is mainly used as a precursor to benzene via hydrodealkylation, C6H5CH3 + H2 → C6H6 + CH4 The second ranked application involves its disproportionation to a mixture of benzene and xylene. When oxidized it yields benzaldehyde and benzoic acid, two important intermediates in chemistry, in addition to the synthesis of benzene and xylene, toluene is a feedstock for toluene diisocyanate, trinitrotoluene, and a number of synthetic drugs. Toluene is a solvent, e. g. for paints, paint thinners, silicone sealants, many chemical reactants, rubber, printing ink, adhesives, lacquers, leather tanners
33.
Gold(III) chloride
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Gold chloride, traditionally called auric chloride, is a chemical compound of gold and chlorine. With the molecular formula Au2Cl6, the name gold trichloride is a simplification, referring to the empirical formula, the Roman numerals in the name indicate that the gold has an oxidation state of +3, which is common for gold compounds. There is also another related chloride of gold, gold chloride, chloroauric acid, HAuCl4, the product formed when gold dissolves in aqua regia, is sometimes referred to as gold chloride or acid gold trichloride. Gold chloride is hygroscopic and highly soluble in water as well as ethanol. It decomposes above 160 °C or in light, AuCl3 exists as a chloride-bridged dimer both as a solid and as a vapour, at least at low temperatures. The structure is similar to that of iodine chloride, in gold chloride, each gold center is square planar, which is typical of a metal complex with a d8 electron count. The bonding in AuCl3 is considered somewhat covalent and its acid, chloroauric acid, is then heated to eliminate hydrogen chloride gas. It may be reduced by Fe2+ causing elemental gold to be precipitated from solution, anhydrous AuCl3 begins to decompose to AuCl at around 160 °C, however, this in turn undergoes disproportionation at higher temperatures to give gold metal and AuCl3. AuCl3 → AuCl + Cl23 AuCl → AuCl3 +2 Au AuCl3 is Lewis acidic and readily forms complexes. For example, it reacts with acid to form chloroauric acid, HCl + AuCl 3 → H+ + − Other chloride sources, such as KCl. Aqueous solutions of AuCl3 react with aqueous base such as sodium hydroxide to form a precipitate of Au3, if gently heated, Au3 decomposes to gold oxide, Au2O3, and then to gold metal. Gold chloride is the point for the synthesis of many other gold compounds. Gold salts, especially Na, provide an alternative to mercury salts as catalysts for reactions involving alkynes, an illustrative reaction is the hydration of terminal alkynes to produce methylketones, Some alkynes undergo amination in the presence of gold catalysts. Gold catalyses the alkylation of aromatic rings and a conversion of furans to phenols. In some cases where alkynes are present, phenols sometimes form, as a stoichiometric reagent, auric chloride reacts with benzene under extremely mild conditions to afford the dimeric phenylgold dichloride, PhH + ½Au2Cl6 → ½2 + HCl
34.
Triflic acid
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Trifluoromethanesulfonic acid, also known as triflic acid, TFMS, TFSA, HOTf or TfOH, is a sulfonic acid with the chemical formula CF3SO3H. It is one of the strongest acids, Triflic acid is mainly used in research as a catalyst for esterification. It is a hygroscopic, colorless, slightly viscous liquid and is soluble in polar solvents and it is also used as an acidic titrant in nonaqueous acid-base titration because it behaves as a strong acid in many solvents where common mineral acids are only moderately strong. With a Ka =5 ×1014, pKa −14.7 and it owes many of its useful properties to its great thermal and chemical stability. Both the acid and its conjugate base CF3SO−3, known as triflate, resist oxidation/reduction reactions, whereas many strong acids are oxidizing, e. g. perchloric or nitric acid. Further recommending its use, triflic acid does not sulfonate substrates, which can be a problem with acid, fluorosulfuric acid. Below is a prototypical sulfonation, which HOTf does not undergo, C6H6 + H2SO4 → C6H5 + H2O Triflic acid fumes in moist air and forms a stable solid monohydrate, CF3SO3H·H2O, the triflate ligand is labile, reflecting its low basicity. Trifluoromethanesulfonic acid exothermically reacts with metal carbonates, hydroxides, and oxides, illustrative is the synthesis of Cu2. Triflic acid reacts with acyl halides to give mixed triflate anhydrides, Triflic acid promotes other Friedel–Crafts-like reactions including the cracking of alkanes and alkylation of alkenes, which are very important to the petroleum industry. These triflic acid derivative catalysts are effective in isomerizing straight chain or slightly branched hydrocarbons that can increase the octane rating of a particular petroleum-based fuel. Triflic acid reacts exothermically with alcohols to produce ethers and olefins, dehydration gives the acid anhydride, trifluoromethanesulfonic anhydride, 2O. Trifluoromethanesulfonic acid is one of the strongest acids, contact with skin causes severe burns with delayed tissue destruction. On inhalation it causes fatal spasms, inflammation and edema, addition of triflic acid to polar solvents can be dangerously exothermic
35.
Absorption spectroscopy
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Absorption spectroscopy refers to spectroscopic techniques that measure the absorption of radiation, as a function of frequency or wavelength, due to its interaction with a sample. The sample absorbs energy, i. e. photons, from the radiating field, the intensity of the absorption varies as a function of frequency, and this variation is the absorption spectrum. Absorption spectroscopy is performed across the electromagnetic spectrum, Infrared and ultraviolet-visible spectroscopy are particularly common in analytical applications. Absorption spectroscopy is employed in studies of molecular and atomic physics, astronomical spectroscopy. There are a range of experimental approaches for measuring absorption spectra. The most common arrangement is to direct a beam of radiation at a sample. The transmitted energy can be used to calculate the absorption, the source, sample arrangement and detection technique vary significantly depending on the frequency range and the purpose of the experiment. A materials absorption spectrum is the fraction of incident radiation absorbed by the material over a range of frequencies, the absorption spectrum is primarily determined by the atomic and molecular composition of the material. Radiation is more likely to be absorbed at frequencies that match the difference between two quantum mechanical states of the molecules. The absorption that occurs due to a transition between two states is referred to as a line and a spectrum is typically composed of many lines. The frequencies where absorption lines occur, as well as their relative intensities, primarily depend on the electronic, the frequencies will also depend on the interactions between molecules in the sample, the crystal structure in solids, and on several environmental factors. The lines will also have a width and shape that are determined by the spectral density or the density of states of the system. Absorption lines are classified by the nature of the quantum mechanical change induced in the molecule or atom. Rotational lines, for instance, occur when the state of a molecule is changed. Rotational lines are found in the microwave spectral region. Vibrational lines correspond to changes in the state of the molecule and are typically found in the infrared region. Electronic lines correspond to a change in the state of an atom or molecule and are typically found in the visible. X-ray absorptions are associated with the excitation of inner shell electrons in atoms and these changes can also be combined, leading to new absorption lines at the combined energy of the two changes
36.
Fluorescence spectroscopy
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Fluorescence spectroscopy is a type of electromagnetic spectroscopy that analyzes fluorescence from a sample. A complementary technique is absorption spectroscopy, in the special case of single molecule fluorescence spectroscopy, intensity fluctuations from the emitted light are measured from either single fluorophores, or pairs of fluorophores. Devices that measure fluorescence are called fluorometers, molecules have various states referred to as energy levels. Fluorescence spectroscopy is concerned with electronic and vibrational states. Generally, the species being examined has an electronic state of interest. Within each of these states there are various vibrational states. In fluorescence, the species is first excited, by absorbing a photon, collisions with other molecules cause the excited molecule to lose vibrational energy until it reaches the lowest vibrational state of the excited electronic state. This process is often visualized with a Jablonski diagram, the molecule then drops down to one of the various vibrational levels of the ground electronic state again, emitting a photon in the process. As molecules may drop down into any of several levels in the ground state, the emitted photons will have different energies. For atomic species, the process is similar, however, since atomic species do not have energy levels. This process of re-emitting the absorbed photon is resonance fluorescence and while it is characteristic of atomic fluorescence, is seen in molecular fluorescence as well, an emission map is measured by recording the emission spectra resulting from a range of excitation wavelengths and combining them all together. This is a three dimensional surface data set, emission intensity as a function of excitation and emission wavelengths, both types use the following scheme, the light from an excitation source passes through a filter or monochromator, and strikes the sample. A proportion of the incident light is absorbed by the sample, the fluorescent light is emitted in all directions. Various light sources may be used as sources, including lasers, LED. A laser only emits light of high irradiance at a narrow wavelength interval, typically under 0.01 nm. The disadvantage of this method is that the wavelength of a laser cannot be changed by much, a mercury vapor lamp is a line lamp, meaning it emits light near peak wavelengths. By contrast, an arc has a continuous emission spectrum with nearly constant intensity in the range from 300-800 nm. Filters and/or monochromators may be used in fluorimeters, a monochromator transmits light of an adjustable wavelength with an adjustable tolerance
37.
Aromaticity
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Aromatic molecules are very stable, and do not break apart easily to react with other substances. Organic compounds that are not aromatic are classified as aliphatic compounds—they might be cyclic, since the most common aromatic compounds are derivatives of benzene, the word “aromatic” occasionally refers informally to benzene derivatives, and so it was first defined. Nevertheless, many aromatic compounds exist. In living organisms, for example, the most common aromatic rings are the bases in RNA and DNA. An aromatic functional group or other substituent is called an aryl group, the earliest use of the term aromatic was in an article by August Wilhelm Hofmann in 1855. Hofmann used the term for a class of compounds, many of which have odors. In terms of the nature of the molecule, aromaticity describes a conjugated system often made of alternating single and double bonds in a ring. This configuration allows for the electrons in the pi system to be delocalized around the ring, increasing the molecules stability. The molecule cannot be represented by one structure, but rather a hybrid of different structures. These molecules cannot be found in one of these representations, with the longer single bonds in one location. Rather, the molecule exhibits bond lengths in between those of single and double bonds and this commonly seen model of aromatic rings, namely the idea that benzene was formed from a six-membered carbon ring with alternating single and double bonds, was developed by August Kekulé. The model for benzene consists of two forms, which corresponds to the double and single bonds superimposing to produce six one-and-a-half bonds. Benzene is a stable molecule than would be expected without accounting for charge delocalization. As is standard for resonance diagrams, the use of an arrow indicates that two structures are not distinct entities but merely hypothetical possibilities. Neither is a representation of the actual compound, which is best represented by a hybrid of these structures. A C=C bond is shorter than a C−C bond, but benzene is perfectly hexagonal—all six carbon–carbon bonds have the same length, intermediate between that of a single and that of a double bond. In a cyclic molecule with three alternating double bonds, cyclohexatriene, the length of the single bond would be 1.54 Å. However, in a molecule of benzene, the length of each of the bonds is 1.40 Å, a better representation is that of the circular π-bond, in which the electron density is evenly distributed through a π-bond above and below the ring
38.
Energy level
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A quantum mechanical system or particle that is bound—that is, confined spatially—can only take on certain discrete values of energy. This contrasts with classical particles, which can have any energy and these discrete values are called energy levels. The energy spectrum of a system with discrete energy levels is said to be quantized. In chemistry and atomic physics, a shell, or a principal energy level. The closest shell to the nucleus is called the 1 shell, followed by the 2 shell, then the 3 shell, the shells correspond with the principal quantum numbers or are labeled alphabetically with letters used in the X-ray notation. Each shell can contain only a number of electrons, The first shell can hold up to two electrons, the second shell can hold up to eight electrons, the third shell can hold up to 18. The general formula is that the nth shell can in principle hold up to 2 electrons, since electrons are electrically attracted to the nucleus, an atoms electrons will generally occupy outer shells only if the more inner shells have already been completely filled by other electrons. However, this is not a requirement, atoms may have two or even three incomplete outer shells. For an explanation of why electrons exist in these shells see electron configuration, if the potential energy is set to zero at infinite distance from the atomic nucleus or molecule, the usual convention, then bound electron states have negative potential energy. If an atom, ion, or molecule is at the lowest possible level, it. If it is at an energy level, it is said to be excited. If more than one quantum state is at the same energy. They are then called degenerate energy levels, quantized energy levels result from the relation between a particles energy and its wavelength. For a confined particle such as an electron in an atom, only stationary states with energies corresponding to integral numbers of wavelengths can exist, for other states the waves interfere destructively, resulting in zero probability density. Elementary examples that show mathematically how energy levels come about are the particle in a box, the first evidence of quantization in atoms was the observation of spectral lines in light from the sun in the early 1800s by Joseph von Fraunhofer and William Hyde Wollaston. The notion of levels was proposed in 1913 by Danish physicist Niels Bohr in the Bohr theory of the atom. The modern quantum mechanical theory giving an explanation of these levels in terms of the Schrödinger equation was advanced by Erwin Schrödinger and Werner Heisenberg in 1926. When the electron is bound to the atom in any closer value of n, assume there is one electron in a given atomic orbital in a hydrogen-like atom
39.
Ion
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An ion is an atom or a molecule in which the total number of electrons is not equal to the total number of protons, giving the atom or molecule a net positive or negative electrical charge. Ions can be created, by chemical or physical means. In chemical terms, if an atom loses one or more electrons. If an atom gains electrons, it has a net charge and is known as an anion. Ions consisting of only a single atom are atomic or monatomic ions, because of their electric charges, cations and anions attract each other and readily form ionic compounds, such as salts. In the case of ionization of a medium, such as a gas, which are known as ion pairs are created by ion impact, and each pair consists of a free electron. The word ion comes from the Greek word ἰόν, ion, going and this term was introduced by English physicist and chemist Michael Faraday in 1834 for the then-unknown species that goes from one electrode to the other through an aqueous medium. Faraday also introduced the words anion for a charged ion. In Faradays nomenclature, cations were named because they were attracted to the cathode in a galvanic device, arrhenius explanation was that in forming a solution, the salt dissociates into Faradays ions. Arrhenius proposed that ions formed even in the absence of an electric current, ions in their gas-like state are highly reactive, and do not occur in large amounts on Earth, except in flames, lightning, electrical sparks, and other plasmas. These gas-like ions rapidly interact with ions of charge to give neutral molecules or ionic salts. These stabilized species are commonly found in the environment at low temperatures. A common example is the present in seawater, which are derived from the dissolved salts. Electrons, due to their mass and thus larger space-filling properties as matter waves, determine the size of atoms. Thus, anions are larger than the parent molecule or atom, as the excess electron repel each other, as such, in general, cations are smaller than the corresponding parent atom or molecule due to the smaller size of its electron cloud. One particular cation contains no electrons, and thus consists of a single proton - very much smaller than the parent hydrogen atom. Since the electric charge on a proton is equal in magnitude to the charge on an electron, an anion, from the Greek word ἄνω, meaning up, is an ion with more electrons than protons, giving it a net negative charge. A cation, from the Greek word κατά, meaning down, is an ion with fewer electrons than protons, there are additional names used for ions with multiple charges
40.
Polyvinyl alcohol
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Poly is a water-soluble synthetic polymer. It has the formula n. It is used in papermaking, textiles, and a variety of coatings and it is sometimes supplied as beads or as solutions in water. Polyvinyl acetals, Polyvinyl acetals are prepared by reacting aldehydes with polyvinyl alcohol, Polyvinyl butyral and polyvinyl formal are examples of this family of polymers. They are prepared from polyvinyl alcohol by reaction with butyraldehyde and formaldehyde, preparation of polyvinyl butyral is the largest use for polyvinyl alcohol in the U. S. and Western Europe. Polyvinyl alcohol is used as a polymerization aid, as protective colloid. This is the largest market application in China, in Japan its major use is vinylon fiber production. An example is the envelope containing laundry detergent in liqui-tabs, feminine hygiene and adult incontinence products as a biodegradable plastic backing sheet. PVA is widely used in sport fishing. Small bags made from PVA are filled with dry or oil based bait and attached to the hook, or the hook is placed inside the bag. When the bag lands on the lake or river bottom it dissolves in water, leaving the hook bait surrounded by ground bait and this method helps attract fish to the hook bait. Anglers also use string made of PVA for the purpose of making temporary attachments, for example, holding a length of line in a coil, that might otherwise tangle while the cast is made. Unlike most vinyl polymers, PVA is not prepared by polymerization of the corresponding monomer, the monomer, vinyl alcohol, is unstable with respect to acetaldehyde. PVA instead is prepared by first polymerizing vinyl acetate, and the resulting polyvinylacetate is converted to the PVA, other precursor polymers are sometimes used, with formate, chloroacetate groups instead of acetate. Worldwide consumption of alcohol was over one million metric tons in 2006. The North Korean-manufacture fiber Vinalon is produced from polyvinyl alcohol, despite its inferior properties as a clothing fiber, it is produced for self-sufficiency reasons, because no oil is required to produce it. PVA is a material that exhibits crystallinity. In terms of microstructure, it is composed mainly of 1, 3-diol linkages but a few percent of 1, 2-diols occur, Polyvinyl alcohol has excellent film forming, emulsifying and adhesive properties
41.
PH
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In chemistry, pH is a numeric scale used to specify the acidity or basicity of an aqueous solution. It is approximately the negative of the base 10 logarithm of the concentration, measured in units of moles per liter. More precisely it is the negative of the logarithm to base 10 of the activity of the hydrogen ion, solutions with a pH less than 7 are acidic and solutions with a pH greater than 7 are basic. Pure water is neutral, at pH7, being neither an acid nor a base, contrary to popular belief, the pH value can be less than 0 or greater than 14 for very strong acids and bases respectively. The pH scale is traceable to a set of standard solutions whose pH is established by international agreement, the pH of aqueous solutions can be measured with a glass electrode and a pH meter, or an indicator. In the first papers, the notation had the H as a subscript to the p, as so. The exact meaning of the p in pH is disputed, but according to the Carlsberg Foundation and it has also been suggested that the p stands for the German Potenz, others refer to French puissance. Another suggestion is that the p stands for the Latin terms pondus hydrogenii, potentia hydrogenii and it is also suggested that Sørensen used the letters p and q simply to label the test solution and the reference solution. Currently in chemistry, the p stands for decimal cologarithm of, PH is defined as the decimal logarithm of the reciprocal of the hydrogen ion activity, aH+, in a solution. P H = − log 10 = log 10 For example and this definition was adopted because ion-selective electrodes, which are used to measure pH, respond to activity. For H+ number of electrons transferred is one and it follows that electrode potential is proportional to pH when pH is defined in terms of activity. The reference electrode may be a silver chloride electrode or a calomel electrode, the hydrogen-ion selective electrode is a standard hydrogen electrode. Reference electrode | concentrated solution of KCl || test solution | H2 | Pt Firstly, the cell is filled with a solution of hydrogen ion activity. Then the emf, EX, of the cell containing the solution of unknown pH is measured. PH = pH + E S − E X z The difference between the two measured emf values is proportional to pH and this method of calibration avoids the need to know the standard electrode potential. The proportionality constant, 1/z is ideally equal to 12.303 R T / F the Nernstian slope, to apply this process in practice, a glass electrode is used rather than the cumbersome hydrogen electrode. A combined glass electrode has a reference electrode. It is calibrated against buffer solutions of hydrogen ion activity
42.
Hydrogen bond
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Hydrogen bonds can occur between molecules or within different parts of a single molecule. Depending on geometry and environment, the hydrogen bond free energy content is between 1 and 5 kcal/mol and this makes it stronger than a van der Waals interaction, but weaker than covalent or ionic bonds. This type of bond can occur in molecules such as water and in organic molecules like DNA. Intermolecular hydrogen bonding is responsible for the boiling point of water compared to the other group 16 hydrides that have much weaker hydrogen bonds. Intramolecular hydrogen bonding is responsible for the secondary and tertiary structures of proteins. It also plays an important role in the structure of polymers, in 2011, an IUPAC Task Group recommended a modern evidence-based definition of hydrogen bonding, which was published in the IUPAC journal Pure and Applied Chemistry. An accompanying detailed technical report provides the rationale behind the new definition, a hydrogen atom attached to a relatively electronegative atom will play the role of the hydrogen bond donor. This electronegative atom is usually fluorine, oxygen, or nitrogen, a hydrogen attached to carbon can also participate in hydrogen bonding when the carbon atom is bound to electronegative atoms, as is the case in chloroform, CHCl3. An example of a hydrogen donor is the hydrogen from the hydroxyl group of ethanol. In a hydrogen bond, the electronegative atom not covalently attached to the hydrogen is named proton acceptor, because of the small size of hydrogen relative to other atoms and molecules, the resulting charge, though only partial, represents a large charge density. A hydrogen bond results when this positive charge density attracts a lone pair of electrons on another heteroatom. The hydrogen bond is described as an electrostatic dipole-dipole interaction. These covalent features are more substantial when acceptors bind hydrogens from more electronegative donors, the partially covalent nature of a hydrogen bond raises the following questions, To which molecule or atom does the hydrogen nucleus belong. And Which should be labeled donor and which acceptor, liquids that display hydrogen bonding are called associated liquids. Hydrogen bonds can vary in strength from weak to extremely strong. For example, the central interresidue N−H···N hydrogen bond between guanine and cytosine is much stronger in comparison to the N−H···N bond between the adenine-thymine pair, the length of hydrogen bonds depends on bond strength, temperature, and pressure. The bond strength itself is dependent on temperature, pressure, bond angle, the typical length of a hydrogen bond in water is 197 pm. The ideal bond angle depends on the nature of the hydrogen bond donor, moore and Winmill used the hydrogen bond to account for the fact that trimethylammonium hydroxide is a weaker base than tetramethylammonium hydroxide
43.
Chirality (chemistry)
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Chirality /kaɪˈrælɪti/ is a geometric property of some molecules and ions. A chiral molecule/ion is non-superposable on its mirror image, the presence of an asymmetric carbon center is one of several structural features that induce chirality in organic and inorganic molecules. The term chirality is derived from the Greek word for hand, the mirror images of a chiral molecule/ion are called enantiomers or optical isomers. Individual enantiomers are often designated as either right- or left-handed, Chirality is an essential consideration when discussing the stereochemistry in organic and inorganic chemistry. The concept is of practical importance because most biomolecules and pharmaceuticals are chiral. Chirality is based on molecular symmetry elements, specifically, a chiral compound can contain no improper axis of rotation, which includes planes of symmetry and inversion center. Chiral molecules are always dissymmetric but not always asymmetric, in general, chiral molecules have point chirality at a single stereogenic atom, which has four different substituents. The two enantiomers of such compounds are said to have different absolute configurations at this center, the stereogenic atom is usually carbon, as in many biological molecules. However chirality can exist in any atom, including metals, phosphorus, Chiral nitrogen is equally possible, although the effects of nitrogen inversion can make many of these compounds impossible to isolate. While the presence of a stereogenic atom describes the great majority of cases, for instance it is not necessary for the chiral substance to have a stereogenic atom. Examples include 1-bromo-1-chloro-1-fluoroadamantane, methylethylphenyltetrahedrane, certain calixarenes and fullerenes, which have inherent chirality, the C2-symmetric species 1, 1-bi-2-naphthol,1, 3-dichloro-allene have axial chirality. -cyclooctene and many ferrocenes have planar chirality, when the optical rotation for an enantiomer is too low for practical measurement, the species is said to exhibit cryptochirality. Even isotopic differences must be considered when examining chirality, illustrative is the derivative of benzyl alcohol PhCHDOH is chiral. The S enantiomer has D = +0. 715°, many biologically active molecules are chiral, including the naturally occurring amino acids and sugars. In biological systems, most of these compounds are of the chirality, most amino acids are levorotatory. Typical naturally occurring proteins, made of L amino acids, are known as left-handed proteins, d-amino acids are very rare in nature and have only been found in small peptides attached to bacteria cell walls. The origin of this homochirality in biology is the subject of much debate, however, there is some suggestion that early amino acids could have formed in comet dust. Enzymes, which are chiral, often distinguish between the two enantiomers of a chiral substrate, one could imagine an enzyme as having a glove-like cavity that binds a substrate
. PMID 22493452.