The haloalkanes are a group of chemical compounds derived from alkanes containing one or more halogens. They are a subset of the general class of halocarbons, although the distinction is not made. Haloalkanes are used commercially and are known under many chemical and commercial names, they are used as flame retardants, fire extinguishants, propellants and pharmaceuticals. Subsequent to the widespread use in commerce, many halocarbons have been shown to be serious pollutants and toxins. For example, the chlorofluorocarbons have been shown to lead to ozone depletion. Methyl bromide is a controversial fumigant. Only haloalkanes which contain chlorine and iodine are a threat to the ozone layer, but fluorinated volatile haloalkanes in theory may have activity as greenhouse gases. Methyl iodide, a occurring substance, does not have ozone-depleting properties and the United States Environmental Protection Agency has designated the compound a non-ozone layer depleter. For more information, see Halomethane.
Haloalkane or alkyl halides are the compounds which have the general formula "RX" where R is an alkyl or substituted alkyl group and X is a halogen. Haloalkanes have been known for centuries. Chloroethane was produced synthetically in the 15th century; the systematic synthesis of such compounds developed in the 19th century in step with the development of organic chemistry and the understanding of the structure of alkanes. Methods were developed for the selective formation of C-halogen bonds. Versatile methods included the addition of halogens to alkenes, hydrohalogenation of alkenes, the conversion of alcohols to alkyl halides; these methods are so reliable and so implemented that haloalkanes became cheaply available for use in industrial chemistry because the halide could be further replaced by other functional groups. While most haloalkanes are human-produced, non-artificial-source haloalkanes do occur on Earth through enzyme-mediated synthesis by bacteria and sea macroalgae. More than 1600 halogenated organics have been identified, with bromoalkanes being the most common haloalkanes.
Brominated organics in biology range from biologically produced methyl bromide to non-alkane aromatics and unsaturates. Halogenated alkanes in land plants are more rare, but do occur, as for example the fluoroacetate produced as a toxin by at least 40 species of known plants. Specific dehalogenase enzymes in bacteria which remove halogens from haloalkanes, are known. From the structural perspective, haloalkanes can be classified according to the connectivity of the carbon atom to which the halogen is attached. In primary haloalkanes, the carbon that carries the halogen atom is only attached to one other alkyl group. An example is chloroethane. In secondary haloalkanes, the carbon that carries the halogen atom has two C–C bonds. In tertiary haloalkanes, the carbon that carries the halogen atom has three C–C bonds. Haloalkanes can be classified according to the type of halogen on group 7 responding to a specific halogenoalkane. Haloalkanes containing carbon bonded to fluorine, chlorine and iodine results in organofluorine, organochlorine and organoiodine compounds, respectively.
Compounds containing more than one kind of halogen are possible. Several classes of used haloalkanes are classified in this way chlorofluorocarbons, hydrochlorofluorocarbons and hydrofluorocarbons; these abbreviations are common in discussions of the environmental impact of haloalkanes. Haloalkanes resemble the parent alkanes in being colorless odorless, hydrophobic; the melting and boiling points of chloro-, bromo-, iodoalkanes are higher than the analogous alkanes, scaling with the atomic weight and number of halides. This is due to the increased strength of the intermolecular forces—from London dispersion to dipole-dipole interaction because of the increased polarizability, thus carbon tetraiodide is a solid. Many fluoroalkanes, however, go against this trend and have lower melting and boiling points than their nonfluorinated analogues due to the decreased polarizability of fluorine. For example, methane has a melting point of -182.5 °C whereas tetrafluoromethane has a melting point of -183.6 °C.
As they contain fewer C–H bonds, halocarbons are less flammable than alkanes, some are used in fire extinguishers. Haloalkanes are better solvents than the corresponding alkanes because of their increased polarity. Haloalkanes containing halogens other than fluorine are more reactive than the parent alkanes—it is this reactivity, the basis of most controversies. Many are alkylating agents, with primary haloalkanes and those containing heavier halogens being the most active; the ozone-depleting abilities of the CFCs arises from the photolability of the C–Cl bond. Haloalkanes are of wide interest because they are widespread and have diverse beneficial and detrimental impacts; the oceans are estimated to release 1-2 million tons of bromomethane annually. A large number of pharmaceuticals contain halogens fluorine. An estimated one fifth of pharmaceuticals contain fluorine, including several of the most used drugs. Examples include 5-fluorouracil, paroxetine, ciprofloxacin and fluconazole; the beneficial effects arise because the C-F bond is unreactive.
Fluorine-substituted ethers are volatile anesthetics, including the commercial product
The SN2 reaction is a type of reaction mechanism, common in organic chemistry. In this mechanism, one bond is broken and one bond is formed synchronously, i.e. in one step. SN2 is a kind of nucleophilic substitution reaction mechanism. Since two reacting species are involved in the slow step, this leads to the term substitution nucleophilic or SN2, the other major kind is SN1. Many other more specialized mechanisms describe substitution reactions; the reaction type is so common that it has other names, e.g. "bimolecular nucleophilic substitution", or, among inorganic chemists, "associative substitution" or "interchange mechanism". The reaction most occurs at an aliphatic sp3 carbon center with an electronegative, stable leaving group attached to it, a halide atom; the breaking of the C–X bond and the formation of the new bond occur through a transition state in which a carbon under nucleophilic attack is pentacoordinate, sp2 hybridised. The nucleophile attacks the carbon at 180° to the leaving group, since this provides the best overlap between the nucleophile's lone pair and the C–X σ* antibonding orbital.
The leaving group is pushed off the opposite side and the product is formed with inversion of the tetrahedral geometry at the central atom. If the substrate under nucleophilic attack is chiral this leads to inversion of configuration, called a Walden inversion. In an example of the SN2 reaction, the attack of Br− on an ethyl chloride results in ethyl bromide, with chloride ejected as the leaving group.: SN2 attack occurs if the backside route of attack is not sterically hindered by substituents on the substrate. Therefore, this mechanism occurs at unhindered primary and secondary carbon centres. If there is steric crowding on the substrate near the leaving group, such as at a tertiary carbon centre, the substitution will involve an SN1 rather than an SN2 mechanism. Four factors affect the rate of the reaction: The substrate plays the most important part in determining the rate of the reaction; this is because the nucleophile attacks from the back of the substrate, thus breaking the carbon-leaving group bond and forming the carbon-nucleophile bond.
Therefore, to maximise the rate of the SN2 reaction, the back of the substrate must be as unhindered as possible. Overall, this means that methyl and primary substrates react the fastest, followed by secondary substrates. Tertiary substrates do not participate in SN2 reactions, because of steric hindrance. Structures that can form stable cations by simple loss of the leaving group, for example, as a resonance-stabilized carbocation, are likely to react via an SN1 pathway in competition with SN2. Like the substrate, steric hindrance affects the nucleophile's strength; the methoxide anion, for example, is both a strong base and nucleophile because it is a methyl nucleophile, is thus much unhindered. Tert-Butoxide, on the other hand, is a strong base, but a poor nucleophile, because of its three methyl groups hindering its approach to the carbon. Nucleophile strength is affected by charge and electronegativity: nucleophilicity increases with increasing negative charge and decreasing electronegativity.
For example, OH− is a better nucleophile than water, I− is a better nucleophile than Br−. In a polar aprotic solvent, nucleophilicity increases up a column of the periodic table as there is no hydrogen bonding between the solvent and nucleophile. I − would therefore be a weaker nucleophile than Br −. Verdict - A strong/anionic nucleophile always favours SN2 manner of nucleophillic substitution; the solvent affects the rate of reaction because solvents may or may not surround a nucleophile, thus hindering or not hindering its approach to the carbon atom. Polar aprotic solvents, like tetrahydrofuran, are better solvents for this reaction than polar protic solvents because polar protic solvents will hydrogen bond to the nucleophile, hindering it from attacking the carbon with the leaving group. A polar aprotic solvent with low dielectric constant or a hindered dipole end will favour SN2 manner of nucleophilic substitution reaction. Examples: DMSO, DMF, acetone etc. In polar aprotic solvent, nucleophilicity parallels basicity.
The stability of the leaving group as an anion and the strength of its bond to the carbon atom both affect the rate of reaction. The more stable the conjugate base of the leaving group is, the more that it will take the two electrons of its bond to carbon during the reaction. Therefore, the weaker the leaving group is as a conjugate base, thus the stronger its corresponding acid, the better the leaving group. Examples of good leaving groups are therefore the halides and tosylate, whereas HO− and H2N− are not; the rate of an SN2 reaction is second order, as the rate-determining step depends on the nucleophile concentration, as well as the concentration of substrate. R = kThis is a key difference between the SN2 mechanisms. In the SN1 reaction the nucleophile attacks after the rate-limiting step is over, whereas in SN2 the nucleophile forces off the leaving group in the limiting step. In other words, the rate of SN1 reactions depend only on the concentration of the substrate while the SN2 reaction rate depends on the concentration of both the substrate and nucleophile.
It has been shown that except in uncommon primary and secondary
Potassium bromide is a salt used as an anticonvulsant and a sedative in the late 19th and early 20th centuries, with over-the-counter use extending to 1975 in the US. Its action is due to the bromide ion. Potassium bromide is used as an antiepileptic medication for dogs. Under standard conditions, potassium bromide is a white crystalline powder, it is soluble in water. In a dilute aqueous solution, potassium bromide tastes sweet, at higher concentrations it tastes bitter, tastes salty when the concentration is higher; these effects are due to the properties of the potassium ion—sodium bromide tastes salty at any concentration. In high concentration, potassium bromide irritates the gastric mucous membrane, causing nausea and sometimes vomiting. Potassium bromide, a typical ionic salt, is dissociated and near pH 7 in aqueous solution, it serves as a source of bromide ions. This reaction is important for the manufacture of silver bromide for photographic film: KBr + AgNO3 → AgBr + KNO3Aqueous bromide Br− forms complexes when reacted with some metal halides such as copper bromide: 2 KBr + CuBr2 → K2 A traditional method for the manufacture of KBr is the reaction of potassium carbonate with an iron bromide, Fe3Br8, made by treating scrap iron under water with excess bromine: 4 K2CO3 + Fe3Br8 → 8 KBr + Fe3O4 + 4 CO2 The anticonvulsant properties of potassium bromide were first noted by Sir Charles Locock at a meeting of the Royal Medical and Chirurgical Society in 1857.
Bromide can be regarded as the first effective medication for epilepsy. At the time, it was thought that epilepsy was caused by masturbation. Locock noted that bromide calmed sexual excitement and thought this was responsible for his success in treating seizures. In the latter half of the 19th century, potassium bromide was used for the calming of seizure and nervous disorders on an enormous scale, with the use by single hospitals being as much as several tons a year. By the beginning of the 20th century the generic word had become so associated with being sedate that bromide came to mean a dull, sedate person or a boring platitude uttered by such a person. There was not a better epilepsy drug until phenobarbital in 1912; the British Army has been claimed to lace soldiers' tea with bromide to quell sexual arousal but, untrue as doing so would diminish alertness in battle. Similar stories exist about a number of substances. Bromide compounds sodium bromide, remained in over-the-counter sedatives and headache remedies in the US until 1975, when bromides were outlawed in all over-the-counter medicines, due to chronic toxicity.
Bromide's exceedingly long half life in the body made it difficult to dose without side effects. Medical use of bromides in the US was discontinued at this time, as many better and shorter-acting sedatives were known by then. Potassium bromide is used in veterinary medicine to treat epilepsy in dogs, either as first-line treatment or in addition to phenobarbital, when seizures are not adequately controlled with phenobarbital alone. Use of bromide in cats is limited because it carries a substantial risk of causing lung inflammation in them; the use of bromide as a treatment drug for animals means that veterinary medical diagnostic laboratories are able as a matter of routine to measure serum levels of bromide on order of a veterinarian, whereas human medical diagnostic labs in the US do not measure bromide as a routine test. Potassium bromide is not approved by the US Food and Drug Administration for use in humans to control seizures. In Germany, it is still approved as an antiepileptic drug for humans children and adolescents.
These indications include severe forms of generalized tonic-clonic seizures, early-childhood-related Grand-Mal-seizures, severe myoclonic seizures during childhood. Adults who have reacted positively to the drug during childhood/adolescence may continue treatment. Potassium bromide tablets are sold under the brand name Dibro-Be mono; the drug has complete bioavailability, but the bromide ion has a long half life of 12 days in the blood, making bromide salts difficult to adjust and dose. Bromide is not known to interfere with the absorption or excretion of any other anticonvulsant, though it does have strong interactions with chloride in the body, the normal body uptake and excretion of which influences bromide's excretion; the therapeutic index for bromide is small. As with other antiepileptics, sometimes therapeutic doses may give rise to intoxication. Indistinguishable from'expected' side-effects, these include: Bromism These are central nervous system reactions, they may include:depression, somnolence loss of appetite and cachexia, nausea/emesis with exicosis loss of reflexes or pathologic reflexes clonic seizures tremor ataxia loss of neural sensitivity paresis cerebral edema with associated headache and papilledema of the eyes delirium: confusion, abnormal speech, loss of concentration and memory, aggressiveness psychosisAcne-form dermatitis and other forms of skin disease may be seen, as well as mucous hypersecretion in the lungs.
Asthma and rhinitis may worsen. Tongue disorder, aphthous stomatitis, bad breath, constipation occur. Potassium bromide is transparent from the near ultraviolet to long-wave
Temperature is a physical quantity expressing hot and cold. It is measured with a thermometer calibrated in one or more temperature scales; the most used scales are the Celsius scale, Fahrenheit scale, Kelvin scale. The kelvin is the unit of temperature in the International System of Units, in which temperature is one of the seven fundamental base quantities; the Kelvin scale is used in science and technology. Theoretically, the coldest a system can be is when its temperature is absolute zero, at which point the thermal motion in matter would be zero. However, an actual physical system or object can never attain a temperature of absolute zero. Absolute zero is denoted as 0 K on the Kelvin scale, −273.15 °C on the Celsius scale, −459.67 °F on the Fahrenheit scale. For an ideal gas, temperature is proportional to the average kinetic energy of the random microscopic motions of the constituent microscopic particles. Temperature is important in all fields of natural science, including physics, Earth science and biology, as well as most aspects of daily life.
Many physical processes are affected by temperature, such as physical properties of materials including the phase, solubility, vapor pressure, electrical conductivity rate and extent to which chemical reactions occur the amount and properties of thermal radiation emitted from the surface of an object speed of sound is a function of the square root of the absolute temperature Temperature scales differ in two ways: the point chosen as zero degrees, the magnitudes of incremental units or degrees on the scale. The Celsius scale is used for common temperature measurements in most of the world, it is an empirical scale, developed by a historical progress, which led to its zero point 0 °C being defined by the freezing point of water, additional degrees defined so that 100 °C was the boiling point of water, both at sea-level atmospheric pressure. Because of the 100-degree interval, it was called a centigrade scale. Since the standardization of the kelvin in the International System of Units, it has subsequently been redefined in terms of the equivalent fixing points on the Kelvin scale, so that a temperature increment of one degree Celsius is the same as an increment of one kelvin, though they differ by an additive offset of 273.15.
The United States 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 Scots-Irish physicist who first defined it, it is a absolute temperature scale. Its zero point, 0 K, is defined to coincide with the coldest physically-possible temperature, its degrees are defined through thermodynamics. The temperature of absolute zero occurs at 0 K = −273.15 °C, the freezing point of water at sea-level atmospheric pressure occurs at 273.15 K = 0 °C. The International System of Units defines a scale and unit for the kelvin or thermodynamic temperature by using the reliably reproducible temperature of the triple point of water as a second reference point; the triple point is a singular state with its own unique and invariant temperature and pressure, along with, for a fixed mass of water in a vessel of fixed volume, an autonomically and stably self-determining partition into three mutually contacting phases, vapour and solid, dynamically depending only on the total internal energy of the mass of water.
For historical reasons, the triple point temperature of water is fixed at 273.16 units of the measurement increment. There is a variety of kinds of temperature scale, it may be convenient to classify them theoretically based. Empirical temperature scales are 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 glass-walled capillary tube, is dependent on temperature, is the basis of the useful mercury-in-glass thermometer; such scales are valid only within convenient ranges of temperature. For example, above the boiling point of mercury, a mercury-in-glass thermometer is impracticable. Most materials expand with temperature increase, but some materials, such as water, contract with temperature increase over some specific range, they are hardly useful as thermometric materials. A material is of no use as a thermometer near one of its phase-change temperatures, for example its boiling-point.
In spite of these restrictions, most used practical thermometers are of the empirically based kind. It was used for calorimetry, which contributed to the discovery of thermodynamics. Empirical thermometry has serious drawbacks when judged as a basis for theoretical physics. Empirically based thermometers, beyond their base as simple direct measurements of ordinary physical properties of thermometric materials, can be re-calibrated, by use of theoretical physical reasoning, this can extend their range of adequacy. Theoretically-based temperature scales are based directly on theoretical arguments those of thermodynamics, kinetic theory and quantum mechanics, they rely on theoretical properties of idealized materials. They are more or less comparable with feasible physical devices and materials. Theoretically based temperature scales are used to provide calibrating standards for practi
In organic and inorganic chemistry, nucleophilic substitution is a fundamental class of reactions in which an electron rich nucleophile selectively bonds with or attacks the positive or positive charge of an atom or a group of atoms to replace a leaving group. The whole molecular entity of which the electrophile and the leaving group are part is called the substrate; the nucleophile attempts to replace the leaving group as the primary substituent in the reaction itself, as a part of another molecule. The most general form of the reaction may be given as the following: Nuc: + R-LG → R-Nuc + LG:The electron pair from the nucleophile attacks the substrate forming a new bond, while the leaving group departs with an electron pair; the principal product in this case is R-Nuc. The nucleophile may be electrically neutral or negatively charged, whereas the substrate is neutral or positively charged. An example of nucleophilic substitution is the hydrolysis of an alkyl bromide, R-Br, under basic conditions, where the attacking nucleophile is the OH− and the leaving group is Br−.
R-Br + OH− → R-OH + Br−Nucleophilic substitution reactions are commonplace in organic chemistry, they can be broadly categorised as taking place at a saturated aliphatic carbon or at an aromatic or other unsaturated carbon centre. In 1935, Edward D. Hughes and Sir Christopher Ingold studied nucleophilic substitution reactions of alkyl halides and related compounds, they proposed. The two main mechanisms are the SN2 reaction. S stands for chemical substitution, N stands for nucleophilic, the number represents the kinetic order of the reaction. In the SN2 reaction, the addition of the nucleophile and the elimination of leaving group take place simultaneously. SN2 occurs where the central carbon atom is accessible to the nucleophile. In SN2 reactions, there are a few conditions. First of all, the 2 in SN2 implies that there are two concentrations of substances that affect the rate of reaction: substrate and nucleophile; the rate equation for this reaction would be Rate=k. For a SN2 reaction, an aprotic solvent is best, such as acetone, DMF, or DMSO.
Aprotic solvents do not add protons ions into solution. Since this reaction occurs in one step, steric effects drive the reaction speed. In the intermediate step, the nucleophile is 180 degrees from the leaving group and the stereochemistry is inverted as the nucleophile bonds to make the product; because the intermediate is bonded to the nucleophile and leaving group, there is no time for the substrate to rearrange itself: the nucleophile will bond to the same carbon that the leaving group was attached to. A final factor that affects reaction rate is nucleophilicity. By contrast the SN1 reaction involves two steps. SN1 reactions tend to be important when the central carbon atom of the substrate is surrounded by bulky groups, both because such groups interfere sterically with the SN2 reaction and because a substituted carbon forms a stable carbocation. Like SN2 reactions, there are quite a few factors. Instead of having two concentrations that affect the reaction rate, there is only one, substrate.
The rate equation for this would be Rate=k. Since the rate of a reaction is only determined by its slowest step, the rate at which the leaving group "leaves" determines the speed of the reaction; this means. A general rule for what makes a good leaving group is the weaker the conjugate base, the better the leaving group. In this case, halogens are going to be the best leaving groups, while compounds such as amines and alkanes are going to be quite poor leaving groups; as SN2 reactions were affected by sterics, SN1 reactions are determined by bulky groups attached to the carbocation. Since there is an intermediate that contains a positive charge, bulky groups attached are going to help stabilize the charge on the carbocation through resonance and distribution of charge. In this case, tertiary carbocation will react faster than a secondary which will react much faster than a primary, it is due to this carbocation intermediate that the product does not have to have inversion. The nucleophile can therefore create a racemic product.
It is important to use a protic solvent and alcohols, since an aprotic solvent could attack the intermediate and cause unwanted product. It does not matter if the hydrogens from the protic solvent react with the nucleophile since the nucleophile is not involved in the rate determining step. There are many reactions in organic chemistry. Common examples include Organic reductions with hydrides, for exampleR-X → R-H using LiAlH4 hydrolysis reactions such asR-Br + OH− → R-OH + Br− or R-Br + H2O → R-OH + HBr Williamson ether synthesisR-Br + OR'− → R-OR' + Br− The Wenker synthesis, a ring-closing reaction of aminoalcohols; the Finkelstein reaction, a halide exchange reaction. Phosphorus nucleophiles appear in the Michaelis -- Arbuzov reaction; the Kolbe nitrile synthesis, the reaction of alkyl halides with cyanides. An example of a substitution reaction taking place by a so-called borderline mechanism as original
Organic reactions are chemical reactions involving organic compounds. The basic organic chemistry reaction types are addition reactions, elimination reactions, substitution reactions, pericyclic reactions, rearrangement reactions, photochemical reactions and redox reactions. In organic synthesis, organic reactions are used in the construction of new organic molecules; the production of many man-made chemicals such as drugs, food additives, fabrics depend on organic reactions. The oldest organic reactions are combustion of organic fuels and saponification of fats to make soap. Modern organic chemistry starts with the Wöhler synthesis in 1828. In the history of the Nobel Prize in Chemistry awards have been given for the invention of specific organic reactions such as the Grignard reaction in 1912, the Diels-Alder reaction in 1950, the Wittig reaction in 1979 and olefin metathesis in 2005. Organic chemistry has a strong tradition of naming a specific reaction to its inventor or inventors and a long list of so-called named reactions exists, conservatively estimated at 1000.
A old named reaction is the Claisen rearrangement and a recent named reaction is the Bingel reaction. When the named reaction is difficult to pronounce or long as in the Corey-House-Posner-Whitesides reaction it helps to use the abbreviation as in the CBS reduction; the number of reactions hinting at the actual process taking place is much smaller, for example the ene reaction or aldol reaction. Another approach to organic reactions is by type of organic reagent, many of them inorganic, required in a specific transformation; the major types are oxidizing agents such as osmium tetroxide, reducing agents such as Lithium aluminium hydride, bases such as lithium diisopropylamide and acids such as sulfuric acid. Reactions are classified by mechanistic class; these classes are polar and pericyclic. Polar reactions are characterized by the movement of electron pairs from a well-defined source to a well-defined sink. Participating atoms undergo changes in charge, both in the formal sense as well as in terms of the actual electron density.
The vast majority of organic reactions fall under this category. Radical reactions are characterized by species with unpaired electrons and the movement of single electrons. Radical reactions are further divided into chain and nonchain processes. Pericyclic reactions involve the redistribution of chemical bonds along a cyclic transition state. Although electron pairs are formally involved, they move around in a cycle without a true source or sink; these reactions require the continuous overlap of participating orbitals and are governed by orbital symmetry considerations. Of course, some chemical processes may involve steps from two of these categories, so this classification scheme is not straightforward or clear in all cases. Beyond these classes, transition-metal mediated reactions are considered to form a fourth category of reactions, although this category encompasses a broad range of elementary organometallic processes, many of which have little in common. Factors governing organic reactions are the same as that of any chemical reaction.
Factors specific to organic reactions are those that determine the stability of reactants and products such as conjugation and aromaticity and the presence and stability of reactive intermediates such as free radicals and carbanions. An organic compound may consist of many isomers. Selectivity in terms of regioselectivity, diastereoselectivity and enantioselectivity is therefore an important criterion for many organic reactions; the stereochemistry of pericyclic reactions is governed by the Woodward–Hoffmann rules and that of many elimination reactions by the Zaitsev's rule. Organic reactions are important in the production of pharmaceuticals. In a 2006 review it was estimated that 20% of chemical conversions involved alkylations on nitrogen and oxygen atoms, another 20% involved placement and removal of protective groups, 11% involved formation of new carbon-carbon bond and 10% involved functional group interconversions. There is no limit to the number of possible organic reactions and mechanisms.
However, certain general patterns are observed that can be used to describe many common or useful reactions. Each reaction has a stepwise reaction mechanism that explains how it happens, although this detailed description of steps is not always clear from a list of reactants alone. Organic reactions can be organized into several basic types; some reactions fit into more than one category. For example, some substitution reactions follow an addition-elimination pathway; this overview isn't intended to include every single organic reaction. Rather, it is intended to cover the basic reactions. In condensation reactions a small molecule water, is split off when two reactants combine in a chemical reaction; the opposite reaction, when water is consumed in a reaction, is called hydrolysis. Many polymerization reactions are derived from organic reactions, they are divided into addition polymerizations and step-growth polymerizations. In general the stepwise progression of reaction mechanisms can be represented using arrow pushing techniques in which curved arrows are used to track the movement of electrons as starting materials transition to intermediates and products.
Organic reactions can be categorized based on the type of functional group involved in the reaction as a reactant and the functional group, formed as a result of this reaction. For example, in the Fries rearrangement the reactant is an ester and the reaction product an alcohol. An overview of functional g
In organic chemistry, butyl is a four-carbon alkyl radical or substituent group with general chemical formula −C4H9, derived from either of the two isomers of butane. The isomer n-butane can connect in two ways, giving rise to two "-butyl" groups: If it connects at one of the two terminal carbon atoms, it is normal butyl or n-butyl: CH3−CH2−CH2−CH2− If it connects at one of the non-terminal carbon atoms, it is secondary butyl or sec-butyl: CH3−CH2−CH− The second isomer of butane, can connect in two ways, giving rise to two additional groups: If it connects at one of the three terminal carbons, it is isobutyl: 2CH−CH2− If it connects at the central carbon, it is tertiary butyl, tert-butyl or t-butyl: 3C− According to IUPAC nomenclature, "isobutyl", "sec-butyl", "tert-butyl" used to be allowed retained names; the latest guidance changed that: only tert-butyl is kept as preferred prefix, all other butyl-names are removed. In the convention of skeletal formulas, every line ending and line intersection specifies a carbon atom saturated with single-linked hydrogen atoms.
The "R" symbol indicates any other non-specific functional group. Butyl is the largest substituent for which trivial names are used for all isomers; the butyl group's carbon, connected to the rest of the molecule is called the RI or R-prime carbon. The prefixes sec and tert refer to the number of additional side chains connected to the first butyl carbon; the prefix "iso" means "equal" while the prefix'n-' stands for "normal". The four isomers of "butyl acetate" demonstrate these four isomeric configurations. Here, the acetate radical appears in each of the positions where the "R" symbol is used in the chart above: Alkyl radicals are considered as a series, a progression sequenced by the number of carbon atoms involved. In that progression, Butyl is the fourth, the last to be named for its history; the word "butyl" is derived from butyric acid, a four-carbon carboxylic acid found in rancid butter. The name "butyric acid" comes from butter. Subsequent alkyl radicals in the series are named from the Greek number that indicates the number of carbon atoms in the group: pentyl, heptyl, etc.
The tert-butyl substituent is bulky and is used in chemistry for kinetic stabilization, as are other bulky groups such as the related trimethylsilyl group. The effect of the tert-butyl group on the progress of a chemical reaction is called the tert-butyl effect, illustrated in the Diels-Alder reaction below. Compared to a hydrogen substituent, the tert-butyl substituent accelerates the reaction rate by a factor of 240; the tert-butyl effect is an example of steric hindrance