1.
Polymer
–
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
2.
Epoxy
–
Epoxy is either any of the basic components or the cured end products of epoxy resins, as well as a colloquial name for the epoxide functional group. Epoxy resins, also known as polyepoxides, are a class of reactive prepolymers and polymers which contain epoxide groups, Epoxy resins may be reacted either with themselves through catalytic homopolymerisation, or with a wide range of co-reactants including polyfunctional amines, acids, phenols, alcohols and thiols. These co-reactants are often referred to as hardeners or curatives, reaction of polyepoxides with themselves or with polyfunctional hardeners forms a thermosetting polymer, often with high mechanical properties, temperature and chemical resistance. Epoxy resins are low molecular weight pre-polymers or higher molecular weight polymers which contain at least two epoxide groups. The epoxide group is sometimes referred to as a glycidyl or oxirane group. A wide range of epoxy resins are produced industrially, the raw materials for epoxy resin production are today largely petroleum derived, although some plant derived sources are now becoming commercially available. Epoxy resins are polymeric or semi-polymeric materials, and as such rarely exist as pure substances, high purity grades can be produced for certain applications, e. g. using a distillation purification process. One downside of high purity liquid grades is their tendency to form crystalline solids due to their highly regular structure, an important criterion for epoxy resins is the epoxide content. Epoxies are typically cured with stoichiometric or near-stoichiometric quantities of curative to achieve maximum physical properties, use of blending, additives and fillers is often referred to as formulating. Important epoxy resins are produced from combining epichlorohydrin and bisphenol A to give bisphenol A diglycidyl ethers, as the molecular weight of the resin increases, the epoxide content reduces and the material behaves more and more like a thermoplastic. Very high molecular weight polycondensates form a class known as phenoxy resins and these resins do however contain hydroxyl groups throughout the backbone, which may also undergo other cross-linking reactions, e. g. with aminoplasts, phenoplasts and isocyanates. Bisphenol F may also undergo epoxidation in a fashion to bisphenol A. Compared to DGEBA, bisphenol F epoxy resins have lower viscosity and a higher mean epoxy content per gramme, reaction of phenols with formaldehyde and subsequent glycidylation with epichlorohydrin produces epoxidised novolacs, such as epoxy phenol novolacs and epoxy cresol novolacs. These are highly viscous to solid resins with typical mean epoxide functionality of around 2 to 6, the high epoxide functionality of these resins forms a highly crosslinked polymer network displaying high temperature and chemical resistance, but low flexibility. Aliphatic epoxy resins are typically formed by glycidylation of aliphatic alcohols or polyols, the resulting resins may be monofunctional, difunctional, or higher functionality. These resins typically display low viscosity at room temperature and are referred to as reactive diluents. They are rarely used alone, but are employed to modify the viscosity of other epoxy resins. This has led to the term ‘modified epoxy resin’ to denote those containing viscosity-lowering reactive diluents, a related class is cycloaliphatic epoxy resin, which contains one or more cycloaliphatic rings in the molecule
3.
Oxygen
–
Oxygen is a chemical element with symbol O and atomic number 8. It is a member of the group on the periodic table and is a highly reactive nonmetal. By mass, oxygen is the third-most abundant element in the universe, after hydrogen, at standard temperature and pressure, two atoms of the element bind to form dioxygen, a colorless and odorless diatomic gas with the formula O2. This is an important part of the atmosphere and diatomic oxygen gas constitutes 20. 8% of the Earths atmosphere, additionally, as oxides the element makes up almost half of the Earths crust. Most of the mass of living organisms is oxygen as a component of water, conversely, oxygen is continuously replenished by photosynthesis, which uses the energy of sunlight to produce oxygen from water and carbon dioxide. Oxygen is too reactive to remain a free element in air without being continuously replenished by the photosynthetic action of living organisms. Another form of oxygen, ozone, strongly absorbs ultraviolet UVB radiation, but ozone is a pollutant near the surface where it is a by-product of smog. At low earth orbit altitudes, sufficient atomic oxygen is present to cause corrosion of spacecraft, the name oxygen was coined in 1777 by Antoine Lavoisier, whose experiments with oxygen helped to discredit the then-popular phlogiston theory of combustion and corrosion. One of the first known experiments on the relationship between combustion and air was conducted by the 2nd century BCE Greek writer on mechanics, Philo of Byzantium. In his work Pneumatica, Philo observed that inverting a vessel over a burning candle, Philo incorrectly surmised that parts of the air in the vessel were converted into the classical element fire and thus were able to escape through pores in the glass. Many centuries later Leonardo da Vinci built on Philos work by observing that a portion of air is consumed during combustion and respiration, Oxygen was discovered by the Polish alchemist Sendivogius, who considered it the philosophers stone. In the late 17th century, Robert Boyle proved that air is necessary for combustion, English chemist John Mayow refined this work by showing that fire requires only a part of air that he called spiritus nitroaereus. From this he surmised that nitroaereus is consumed in both respiration and combustion, Mayow observed that antimony increased in weight when heated, and inferred that the nitroaereus must have combined with it. Accounts of these and other experiments and ideas were published in 1668 in his work Tractatus duo in the tract De respiratione. Robert Hooke, Ole Borch, Mikhail Lomonosov, and Pierre Bayen all produced oxygen in experiments in the 17th and the 18th century but none of them recognized it as a chemical element. This may have been in part due to the prevalence of the philosophy of combustion and corrosion called the phlogiston theory, which was then the favored explanation of those processes. Established in 1667 by the German alchemist J. J. Becher, one part, called phlogiston, was given off when the substance containing it was burned, while the dephlogisticated part was thought to be its true form, or calx. The fact that a substance like wood gains overall weight in burning was hidden by the buoyancy of the combustion products
4.
Hydrogen peroxide
–
Hydrogen peroxide is a chemical compound with the formula H 2O2. In its pure form, it is a liquid, slightly more viscous than water. Hydrogen peroxide is the simplest peroxide and it is used as an oxidizer, bleaching agent and disinfectant. Concentrated hydrogen peroxide, or high-test peroxide, is an oxygen species and has been used as a propellant in rocketry. Its chemistry is dominated by the nature of its unstable peroxide bond, Hydrogen peroxide is unstable and slowly decomposes in the presence of base or a catalyst. Because of its instability, hydrogen peroxide is typically stored with a stabilizer in an acidic solution. Hydrogen peroxide is found in biological systems including the human body, enzymes that use or decompose hydrogen peroxide are classified as peroxidases. The boiling point of H 2O2 has been extrapolated as being 150.2 °C, in practice hydrogen peroxide will undergo potentially explosive thermal decomposition if heated to this temperature. It may be distilled at lower temperatures under reduced pressure. In aqueous solutions hydrogen peroxide differs from the material due to the effects of hydrogen bonding between water and hydrogen peroxide molecules. Hydrogen peroxide and water form a mixture, exhibiting freezing-point depression, pure water has a melting point of 0 °C. The boiling point of the same mixtures is also depressed in relation with the mean of both boiling points and this boiling point is 14 °C greater than that of pure water and 36.2 °C less than that of pure hydrogen peroxide. Hydrogen peroxide is a molecule with C2 symmetry. Although the O−O bond is a bond, the molecule has a relatively high rotational barrier of 2460 cm−1, for comparison. The increased barrier is ascribed to repulsion between the pairs of the adjacent oxygen atoms and results in hydrogen peroxide displaying atropisomerism. The molecular structures of gaseous and crystalline H 2O2 are significantly different and this difference is attributed to the effects of hydrogen bonding, which is absent in the gaseous state. Crystals of H 2O2 are tetragonal with the space group D4 4P4121, Hydrogen peroxide has several structural analogues with Hm−X−X−Hn bonding arrangements. It has the highest boiling point of this series, diphosphane and hydrogen disulfide exhibit only weak hydrogen bonding and have little chemical similarity to hydrogen peroxide
5.
Chemical reaction
–
A chemical reaction is a process that leads to the transformation of one set of chemical substances to another. Nuclear chemistry is a sub-discipline of chemistry that involves the reactions of unstable. The substance initially involved in a reaction are called reactants or reagents. Chemical reactions are characterized by a chemical change, and they yield one or more products. Reactions often consist of a sequence of individual sub-steps, the elementary reactions. Chemical reactions are described with chemical equations, which present the starting materials, end products. Chemical reactions happen at a characteristic reaction rate at a given temperature, typically, reaction rates increase with increasing temperature because there is more thermal energy available to reach the activation energy necessary for breaking bonds between atoms. Reactions may proceed in the forward or reverse direction until they go to completion or reach equilibrium, Reactions that proceed in the forward direction to approach equilibrium are often described as spontaneous, requiring no input of free energy to go forward. Non-spontaneous reactions require input of energy to go forward. Different chemical reactions are used in combinations during chemical synthesis in order to obtain a desired product, in biochemistry, a consecutive series of chemical reactions form metabolic pathways. These reactions are catalyzed by protein enzymes. Chemical reactions such as combustion in fire, fermentation and the reduction of ores to metals were known since antiquity, in the Middle Ages, chemical transformations were studied by Alchemists. They attempted, in particular, to lead into gold, for which purpose they used reactions of lead. The process involved heating of sulfate and nitrate minerals such as sulfate, alum. In the 17th century, Johann Rudolph Glauber produced hydrochloric acid and sodium sulfate by reacting sulfuric acid, further optimization of sulfuric acid technology resulted in the contact process in the 1880s, and the Haber process was developed in 1909–1910 for ammonia synthesis. From the 16th century, researchers including Jan Baptist van Helmont, Robert Boyle, the phlogiston theory was proposed in 1667 by Johann Joachim Becher. It postulated the existence of an element called phlogiston, which was contained within combustible bodies. This proved to be false in 1785 by Antoine Lavoisier who found the explanation of the combustion as reaction with oxygen from the air
6.
Molecular orbital
–
In chemistry, a molecular orbital is a mathematical function describing the wave-like behavior of an electron in a molecule. This function can be used to calculate chemical and physical properties such as the probability of finding an electron in any specific region, the term orbital was introduced by Robert S. Mulliken in 1932 as an abbreviation for one-electron orbital wave function. At an elementary level, it is used to describe the region of space in which the function has a significant amplitude, Molecular orbitals are usually constructed by combining atomic orbitals or hybrid orbitals from each atom of the molecule, or other molecular orbitals from groups of atoms. They can be calculated using the Hartree–Fock or self-consistent field methods. A molecular orbital can be used to represent the regions in a molecule where an electron occupying that orbital is likely to be found, Molecular orbitals are obtained from the combination of atomic orbitals, which predict the location of an electron in an atom. A molecular orbital can specify the configuration of a molecule. Most commonly a MO is represented as a combination of atomic orbitals. They are invaluable in providing a model of bonding in molecules. Most present-day methods in computational chemistry begin by calculating the MOs of the system, a molecular orbital describes the behavior of one electron in the electric field generated by the nuclei and some average distribution of the other electrons. In the case of two electrons occupying the orbital, the Pauli principle demands that they have opposite spin. Necessarily this is an approximation, and highly accurate descriptions of the electronic wave function do not have orbitals. Molecular orbitals arise from allowed interactions between orbitals, which are allowed if the symmetries of the atomic orbitals are compatible with each other. Efficiency of atomic orbital interactions is determined from the overlap between two atomic orbitals, which is significant if the atomic orbitals are close in energy. Finally, the number of molecular orbitals that form must equal the number of orbitals in the atoms being combined to form the molecule. Here, the orbitals are expressed as linear combinations of atomic orbitals. Molecular orbitals were first introduced by Friedrich Hund and Robert S. Mulliken in 1927 and 1928, the linear combination of atomic orbitals or LCAO approximation for molecular orbitals was introduced in 1929 by Sir John Lennard-Jones. His ground-breaking paper showed how to derive the electronic structure of the fluorine and this qualitative approach to molecular orbital theory is part of the start of modern quantum chemistry. Linear combinations of atomic orbitals can be used to estimate the molecular orbitals that are formed upon bonding between the constituent atoms
7.
Alkoxide
–
An alkoxide is the conjugate base of an alcohol and therefore consists of an organic group bonded to a negatively charged oxygen atom. They can be written as RO−, where R is the organic substituent, alkoxides are strong bases and, when R is not bulky, good nucleophiles and good ligands. Alkoxides, although generally not stable in protic solvents such as water, occur widely as intermediates in various reactions, transition metal alkoxides are widely used for coatings and as catalysts. Enolates are unsaturated alkoxides derived by deprotonation of a C-H bond adjacent to a ketone or aldehyde, the nucleophilic center for simple alkoxides is located on the oxygen, whereas the nucleophilic site on enolates is delocalized onto both carbon and oxygen sites. Phenoxides are close relatives of the alkoxides, in which the group is replaced by a derivative of benzene. Phenol is more acidic than a typical alcohol, thus, phenoxides are correspondingly less basic and they are, however, often easier to handle, and yield derivatives that are more crystalline than those of the alkoxides. Alkoxides can be produced by several routes starting from an alcohol, highly reducing metals react directly with alcohols to give the corresponding metal alkoxide. The alcohol serves as an acid, and hydrogen is produced as a by-product, many other metal and main group halides can be used instead of titanium, for example SiCl4, ZrCl4, and PCl3. Many alkoxides can be prepared by dissolution of the corresponding metals in water-free alcohols in the presence of electroconductive additive. The metals may be Co, Ga, Ge, Hf, Fe, Ni, Nb, Mo, La, Re, Sc, Si, Ti, Ta, W, Y, Zr, etc. The conductive additive may be lithium chloride, quaternary ammonium halide, some examples of metal alkoxides obtained by this technique, Ti4, Nb210, Ta210,2, Re2O36, Re4O612, and Re4O610. Other alcohols can be employed in place of water, in this way one alkoxide can be converted to another, and the process is properly referred to as alcoholysis. The position of the equilibrium can be controlled by the acidity of the alcohol, for example phenols typically react with alkoxides to release alcohols, more simply, the alcoholysis can be controlled by selectively evaporating the more volatile component. In this way, ethoxides can be converted to butoxides, since ethanol is more volatile than butanol, in the transesterification process, metal alkoxides react with esters to bring about an exchange of alkyl groups between metal alkoxide and ester. Sodium methoxide, for example, is used for this purpose. Many metal alkoxide compounds also feature oxo-ligands, oxo-ligands typically arise via the hydrolysis, often accidentally, and via ether elimination,2 LnMOR → 2O + R2O Additionally, low valent metal alkoxides are susceptible to oxidation by air. Characteristically, transition metal alkoxides are polynuclear, that is they contain more than one metal, alkoxides are sterically undemanding and highly basic ligands that tend to bridge metals. Upon the isomorphic substitution of metal atoms close in properties crystalline complexes of variable composition are formed, the metal ratio in such compounds can vary over a broad range
8.
Equilateral triangle
–
In geometry, an equilateral triangle is a triangle in which all three sides are equal. In the familiar Euclidean geometry, equilateral triangles are also equiangular and they are regular polygons, and can therefore also be referred to as regular triangles. Thus these are properties that are unique to equilateral triangles, the three medians have equal lengths. The three angle bisectors have equal lengths, every triangle center of an equilateral triangle coincides with its centroid, which implies that the equilateral triangle is the only triangle with no Euler line connecting some of the centers. For some pairs of triangle centers, the fact that they coincide is enough to ensure that the triangle is equilateral, in particular, A triangle is equilateral if any two of the circumcenter, incenter, centroid, or orthocenter coincide. It is also equilateral if its circumcenter coincides with the Nagel point, for any triangle, the three medians partition the triangle into six smaller triangles. A triangle is equilateral if and only if any three of the triangles have either the same perimeter or the same inradius. A triangle is equilateral if and only if the circumcenters of any three of the triangles have the same distance from the centroid. Morleys trisector theorem states that, in any triangle, the three points of intersection of the adjacent angle trisectors form an equilateral triangle, a version of the isoperimetric inequality for triangles states that the triangle of greatest area among all those with a given perimeter is equilateral. That is, PA, PB, and PC satisfy the inequality that any two of them sum to at least as great as the third. By Eulers inequality, the triangle has the smallest ratio R/r of the circumradius to the inradius of any triangle, specifically. The triangle of largest area of all those inscribed in a circle is equilateral. The ratio of the area of the incircle to the area of an equilateral triangle, the ratio of the area to the square of the perimeter of an equilateral triangle,1123, is larger than that for any other triangle. If a segment splits an equilateral triangle into two regions with equal perimeters and with areas A1 and A2, then 79 ≤ A1 A2 ≤97, in no other triangle is there a point for which this ratio is as small as 2. For any point P in the plane, with p, q, and t from the vertices A, B. For any point P on the circle of an equilateral triangle, with distances p, q. There are numerous triangle inequalities that hold with equality if and only if the triangle is equilateral, an equilateral triangle is the most symmetrical triangle, having 3 lines of reflection and rotational symmetry of order 3 about its center. Its symmetry group is the group of order 6 D3
9.
Stoichiometry
–
Stoichiometry /ˌstɔɪkiˈɒmᵻtri/ is the calculation of relative quantities of reactants and products in chemical reactions. This means that if the amounts of the reactants are known. Conversely, if one reactant has a quantity and the quantity of product can be empirically determined. This is illustrated in the image here, where the equation is. Here, one molecule of methane reacts with two molecules of gas to yield one molecule of carbon dioxide and two molecules of water. Stoichiometry measures these quantitative relationships, and is used to determine the amount of products/reactants that are produced/needed in a given reaction, describing the quantitative relationships among substances as they participate in chemical reactions is known as reaction stoichiometry. In the example above, reaction stoichiometry measures the relationship between the methane and oxygen as they react to form carbon dioxide and water. Gas stoichiometry deals with reactions involving gases, where the gases are at a temperature, pressure. For gases, the ratio is ideally the same by the ideal gas law. In practice, due to the existence of isotopes, molar masses are used instead when calculating the mass ratio, the term stoichiometry was first used by Jeremias Benjamin Richter in 1792 when the first volume of Richters Stoichiometry or the Art of Measuring the Chemical Elements was published. The term is derived from the Greek words στοιχεῖον stoicheion element, in patristic Greek, the word Stoichiometria was used by Nicephorus to refer to the number of line counts of the canonical New Testament and some of the Apocrypha. In general, chemical reactions combine in definite ratios of chemicals, since chemical reactions can neither create nor destroy matter, nor transmute one element into another, the amount of each element must be the same throughout the overall reaction. Chemical reactions, as unit operations, consist of simply a very large number of elementary reactions. As the reacting molecules consist of a set of atoms in an integer ratio. A reaction may consume more than one molecule, and the number counts this number, defined as positive for products. Different elements have a different atomic mass, and as collections of atoms, molecules have a definite molar mass. By definition, carbon-12 has a mass of 12 g/mol. The mass ratios can be calculated by dividing each by the total in the whole reaction, Elements in their natural state are mixtures of isotopes of differing mass, thus atomic masses and thus molar masses are not exactly integers
10.
Ether
–
Ethers are a class of organic compounds that contain an ether group—an oxygen atom connected to two alkyl or aryl groups. They have the general formula R–O–R′, where R and R′ represent the alkyl or aryl groups, a typical example of the first group is the solvent and anesthetic diethyl ether, commonly referred to simply as ether. Ethers are common in chemistry and pervasive in biochemistry, as they are common linkages in carbohydrates. Ethers feature C–O–C linkage defined by an angle of about 110°. The barrier to rotation about the C–O bonds is low, the bonding of oxygen in ethers, alcohols, and water is similar. In the language of valence bond theory, the hybridization at oxygen is sp3, oxygen is more electronegative than carbon, thus the hydrogens alpha to ethers are more acidic than in simple hydrocarbons. They are far less acidic than hydrogens alpha to carbonyl groups, depending on the groups at R and R′, ethers are classified into two types, Simple ethers or symmetrical ethers, e. g. diethyl ether, dimethyl ether, etc. Mixed ethers or unsymmetrical ethers, e. g. methyl ethyl ether, methyl phenyl ether, in the IUPAC nomenclature system, ethers are named using the general formula alkoxyalkane, for example CH3–CH2–O–CH3 is methoxyethane. If the ether is part of a complex molecule, it is described as an alkoxy substituent. The simpler alkyl radical is written in front, so CH3–O–CH2CH3 would be given as methoxyethane, IUPAC rules are often not followed for simple ethers. The trivial names for simple ethers are a composite of the two followed by ether. For example, ethyl ether, diphenylether. As for other compounds, very common ethers acquired names before rules for nomenclature were formalized. Diethyl ether is called ether, but was once called sweet oil of vitriol. Methyl phenyl ether is anisole, because it was found in aniseed. Acetals are another class of ethers with characteristic properties, polyethers are compounds with more than one ether group. The crown ethers are examples of small polyethers, some toxins produced by dinoflagellates such as brevetoxin and ciguatoxin are extremely large and are known as cyclic or ladder polyethers. Polyether generally refers to polymers which contain the functional group in their main chain
11.
Functional group
–
In organic chemistry, functional groups are specific groups of atoms or bonds within molecules that are responsible for the characteristic chemical reactions of those molecules. The same functional group will undergo the same or similar chemical reaction regardless of the size of the molecule it is a part of, however, its relative reactivity can be modified by other functional groups nearby. The atoms of functional groups are linked to other and to the rest of the molecule by covalent bonds. Any subgroup of atoms of a compound also may be called a radical, and if a covalent bond is broken homolytically, Functional groups can also be charged, e. g. in carboxylate salts, which turns the molecule into a polyatomic ion or a complex ion. Complexation and solvation is also caused by interactions of functional groups. In the common rule of thumb like dissolves like, it is the shared or mutually well-interacting functional groups give rise to solubility. For example, sugar dissolves in water because both share the functional group and hydroxyls interact strongly with each other. Combining the names of groups with the names of the parent alkanes generates what is termed a systematic nomenclature for naming organic compounds. In traditional nomenclature, the first carbon atom after the carbon that attaches to the group is called the alpha carbon, the second, beta carbon. IUPAC conventions call for numeric labeling of the position, e. g. 4-aminobutanoic acid, in traditional names various qualifiers are used to label isomers, for example isopropanol is an isomer is n-propanol. The following is a list of functional groups. In the formulas, the symbols R and R usually denote an attached hydrogen, or a side chain of any length. Functional groups, called hydrocarbyl, that only carbon and hydrogen. Each one differs in type of reactivity, there are also a large number of branched or ring alkanes that have specific names, e. g. tert-butyl, bornyl, cyclohexyl, etc. Hydrocarbons may form charged structures, positively charged carbocations or negative carbanions, examples are tropylium and triphenylmethyl cations and the cyclopentadienyl anion. Haloalkanes are a class of molecule that is defined by a carbon–halogen bond and this bond can be relatively weak or quite stable. In general, with the exception of fluorinated compounds, haloalkanes readily undergo nucleophilic substitution reactions or elimination reactions, the substitution on the carbon, the acidity of an adjacent proton, the solvent conditions, etc. all can influence the outcome of the reactivity. Compounds that contain nitrogen in this category may contain C-O bonds, compounds that contain sulfur exhibit unique chemistry due to their ability to form more bonds than oxygen, their lighter analogue on the periodic table
12.
Alkene
–
In organic chemistry, an alkene is an unsaturated hydrocarbon that contains at least one carbon–carbon double bond. The words alkene, olefin, and olefine are used often interchangeably, acyclic alkenes, with only one double bond and no other functional groups, known as mono-enes, form a homologous series of hydrocarbons with the general formula CnH2n. Alkenes have two hydrogen atoms less than the corresponding alkane, the simplest alkene, ethylene, with the International Union of Pure and Applied Chemistry name ethene, is the organic compound produced on the largest scale industrially. Aromatic compounds are drawn as cyclic alkenes, but their structure and properties are different. This double bond is stronger than a single covalent bond and also shorter, each carbon of the double bond uses its three sp2 hybrid orbitals to form sigma bonds to three atoms. The unhybridized 2p atomic orbitals, which lie perpendicular to the created by the axes of the three sp² hybrid orbitals, combine to form the pi bond. This bond lies outside the main C–C axis, with half of the bond on one side of the molecule, rotation about the carbon–carbon double bond is restricted because it incurs an energetic cost to break the alignment of the p orbitals on the two carbon atoms. As a consequence, substituted alkenes may exist as one of two isomers, called cis or trans isomers, more complex alkenes may be named with the E–Z notation for molecules with three or four different substituents. For example, of the isomers of butene, the two groups of -but-2-ene appear on the same side of the double bond, and in -but-2-ene the methyl groups appear on opposite sides. These two isomers of butene are slightly different in their chemical and physical properties, a 90° twist of the C=C bond requires less energy than the strength of a pi bond, and the bond still holds. This contradicts a common assertion that the p orbitals would be unable sustain such a bond. In truth, the misalignment of the p orbitals is less than expected because pyramidalization takes place, trans-Cyclooctene is a stable strained alkene and the orbital misalignment is only 19° with a dihedral angle of 137° and a degree of pyramidalization of 18°. The trans isomer of cycloheptene is stable only at low temperatures, as predicted by the VSEPR model of electron pair repulsion, the molecular geometry of alkenes includes bond angles about each carbon in a double bond of about 120°. The angle may vary because of steric strain introduced by nonbonded interactions between groups attached to the carbons of the double bond. For example, the C–C–C bond angle in propylene is 123. 9°, for bridged alkenes, Bredts rule states that a double bond cannot occur at the bridgehead of a bridged ring system unless the rings are large enough. The physical properties of alkenes and alkanes are similar and they are colourless, nonpolar, combustable, and almost odorless. The physical state depends on mass, like the corresponding saturated hydrocarbons, the simplest alkenes, ethene, propene. Linear alkenes of approximately five to sixteen carbons are liquids, Alkenes are relatively stable compounds, but are more reactive than alkanes, either because of the reactivity of the carbon–carbon pi-bond or the presence of allylic CH centers
