An elimination reaction is a type of organic reaction in which two substituents are removed from a molecule in either a one or two-step mechanism. Either the unsaturation of the molecule increases (as in most organic elimination reactions) or the valence of an atom in the molecule decreases by two, a process known as reductive elimination. An important class of elimination reactions are those involving alkyl halides, or alkanes in general, with good leaving groups, reacting with a Lewis base to form an alkene in the reverse of an addition reaction. When the substrate is asymmetric, regioselectivity is determined by Zaitsev's rule. The one and two-step mechanisms are named and known as E2 reaction and E1 reaction, respectively. Organic reactions are chemical reactions between organic compounds. ... In organic chemistry, a substituent is an atom or group of atoms substituted in place of a hydrogen atom on the parent chain of a hydrocarbon. ... A unsaturated compound in chemistry is a chemical compound that contains carbon - carbon pi bonds such as a alkene or a alkyne. ... Oxidative addition and reductive elimination are two important classes of reactions in organometallic chemistry. ... In chemistry, an alkyl halide is an organic molecule of the form R_X, where X is a halide and R contains a carbon atom bonded to other functional groups or hydrogens. ... A leaving group is an atom or molecule that detaches from an organic molecule, which, after detachment, is called the residual or main part. ... A Lewis base is any molecule or ion that can form a new covalent bond by donating a pair of electrons. ... The chemical structure of ethylene, the simplest alkene. ... An addition reaction, in chemistry, is in its simplest terms an organic reaction where two or more molecules combine to form a larger one. ... In chemistry, regioselectivity is the preference of one direction of chemical bond making or breaking over all other possible directions. ... In chemistry, Zaitsevs rule, Saytzeffs rule or Saytsevs rule named after Alexander Mikhailovich Zaitsev (number of different spellings due to name being transliterated from Russian) is a rule that states that if more than one alkene can be formed by an elimination reaction, the more stable alkene...

E2 mechanism

In the 1920s, Sir Christopher Ingold proposed a model to explain a peculiar type of chemical reaction: the E2 mechanism. E2 stands for bimolecular elimination and has the following specificities. Sir Christopher Kelk Ingold (1893-1970) was a British chemist. ...

• It is a one-step process of elimination with a single transition state.
• Typical of secondary or tertiary substituted alkyl halides. It is also observable with primary alkyl halides if a hindered base is used.
• The reaction rate, influenced by both the alkyl halide and the base, is second order.
• Because E2 mechanism results in the formation of a Pi bond, the two leaving groups (often a hydrogen and a halogen) need to be coplanar. An antiperiplanar transition state has staggered conformation with lower energy and a synperiplanar transition state is in eclipsed conformation with higher energy. The reaction mechanism involving staggered conformation is more favourable for E2 reactions.
• Reaction often present with strong base.
• In order for the pi bond to be created, the hybridization of carbons need to be lowered from sp³ to sp².
• The C-H bond is weakened in the rate determining step and therefore the deuterium isotope effect is larger than 1.
• This reaction type has similarities with the S_N2 reaction mechanism.

Saturated (sp³-hybridized) carbons will not react as readily with E2 and it will with E1 due to the steric hindrince. If S_N1 and E1 are competing for the reaction, the E2 can be achieved by increasing the heat. The transition state of a chemical reaction is a particular configuration along the reaction coordinate. ... Iron rusting - a chemical reaction with a slow reaction rate. ... A rate law is an equation that relates concentrations of reactants to the reaction rate. ... The halogens or halogen elements are a series of nonmetal elements from Group 17 (old-style: VII or VIIA; Group 7 IUPAC Style) of the periodic table, comprising fluorine, F, chlorine, Cl, bromine, Br, iodine, I, and astatine, At. ... A set of points is said to be coplanar if and only if they lie on the same geometric plane. ... Alkane stereochemistry concerns the stereochemistry of linear alkanes and the linear alkane conformers. ... The transition state of a chemical reaction is a particular configuration along the reaction coordinate. ... In chemistry a staggered conformation is a chemical conformation that exists in any open chain single chemical bond connecting two sp3 hybridised atoms as a conformational energy minimum. ... Alkane stereochemistry concerns the stereochemistry of linear alkanes and the linear alkane conformers. ... In chemistry an eclipsed conformation is a chemical conformation that exists in any open chain single chemical bond connecting two sp3 hybridised atoms as a conformational energy maximum due to steric hindrance. ... Acids and bases: Acid-base reaction theories pH Self-ionization of water Buffer solutions Systematic naming Electrochemistry Acid-base extraction Acids: Strong acids Weak acids Mineral acids Organic acids Bases: Strong bases Weak bases Organic bases edit In chemistry, a base is most commonly thought of as a substance that... In chemistry, hybridisation is the mixing of atomic orbitals to form new orbitals suitable for bonding. ... The rate-determining step is a chemistry term for the slowest step in a chemical reaction. ... The kinetic isotope effect is a variation in the rate of a chemical reaction when an atom in one of the reactants is replaced by one of its isotopes. ... The SN2 reaction is a type of nucleophilic substitution, where a nucleophile attacks an electrophilic center and bonds to it, expelling another group called a leaving group. ...

The reaction fundamental elements are

• Breaking of the carbon-hydrogen and carbon-halogen bonds in one step.
• Formation of a carbon=carbon Pi bond.

An example of this type of reaction in scheme 1 is the reaction of isobutylbromide with potassium ethoxide in ethanol. The reaction products are isobutylene, ethanol and potassium bromide. Geometry of the water molecule Molecular geometry or molecular structure is the three dimensional arrangement of the atoms that constitute a molecule, inferred from the spectroscopic studies of the compound. ... Image File history File links Download high resolution version (872x316, 5 KB) Summary E2 reaction Licensing I, the creator of this work, hereby grant the permission to copy, distribute and/or modify this document under the terms of the GNU Free Documentation License, Version 1. ... Isobutyl (Common Name) or 2-Methylpropyl (IUPAC) is a substituent group with the formula C4H9. ... General Name, Symbol, Number potassium, K, 19 Chemical series alkali metals Group, Period, Block 1, 4, s Appearance silvery white Atomic mass 39. ... An alkoxide is the conjugate base of an alcohol and therefore consists of an organic group bonded to a negatively charged oxygen atom. ... Ethanol, also known as ethyl alcohol, drinking alcohol or grain alcohol, is a flammable, colorless, slightly toxic chemical compound with a distinctive perfume-like odor, and is the alcohol found in alcoholic beverages. ... 1-butene cis-2-butene trans-2-butene methylpropene There are four alkenes which have four carbon atoms and one double bond in their chemical structure. ... Ethanol, also known as ethyl alcohol, drinking alcohol or grain alcohol, is a flammable, colorless, slightly toxic chemical compound with a distinctive perfume-like odor, and is the alcohol found in alcoholic beverages. ... Potassium bromide (KBr) is a salt, used as an anticonvulsant and a sedative in the 1800s. ...

E1 mechanism

E1 is a model to explain a particular type of chemical elimination reaction. E1 stands for unimolecular elimination and has the following specificities.

• It is a two-step process of elimination ionization and deprotonation.
  • Ionization, Carbon-halogen breaks to give a carbocation intermediate.
  • Deprotonation of the carbocation.
• Typical of tertiary and some secondary substituted alkyl halides.
• The reaction rate is influenced only by the concentration of the alkyl halide because carbocation formation is the slowest, rate-determining step. Therefore first order kinetics apply.
• Reaction mostly occurs in complete absence of base or presence of only weak base.
• E1 reactions are in competition with S_N1 reactions because they share a common carbocationic intermediate.
• Deuterium isotope effect is absent.
• accompanied by carbocationic rearrangement reactions

An example in scheme 2 is the reaction of tert-butylbromide with potassium ethoxide in ethanol. Ionization is the physical process of converting an atom or molecule into an ion by changing the difference between the number of protons and electrons. ... A carbocation (IPA pronunciation: ) is an ion with a positively-charged carbon atom. ... Deprotonation is a chemistry term that refers to the removal of a proton (hydrogen ion H+) from a molecule, forming the conjugate base. ... The rate-determining step is a chemistry term for the slowest step in a chemical reaction. ... A rate law is an equation that relates concentrations of reactants to the reaction rate. ... The SN1 reaction is an substitution reaction in organic chemistry. ... The kinetic isotope effect is a variation in the rate of a chemical reaction when an atom in one of the reactants is replaced by one of its isotopes. ... A rearrangement reaction is a broad class of organic reactions where the carbon skeleton of a molecule is rearranged to give a structural isomer of the original molecule. ... Image File history File links Download high resolution version (1029x293, 6 KB) Summary E1 reaction Licensing I, the creator of this work, hereby grant the permission to copy, distribute and/or modify this document under the terms of the GNU Free Documentation License, Version 1. ...

E1 eliminations happen with highly substituted alkyl halides due to 2 main reasons.

• Highly substituted alkyl halides are bulky, limiting the room for the E2 one-step mechanism; therefore, the two-step E1 mechanism is favored.
• Highly substituted carbocations are more stable than methyl or primary substituted. Such stability gives time for the two-step E1 mechanism to occur.

E2 and E1 elimination final notes

The reaction rate is influenced by halogens reactivity; iodide and bromide being favored. Fluoride is too reactive and its level of basicity too high. There is a certain level of competition between elimination reaction and nucleophilic substitution. More precisely, there are competitions between E2 and S_N2 and also between E1 and S_N1. Substitution generally predominates and elimination occurs only during precise circumstances. Generally, elimination is favored over substitution when Iron rusting - a chemical reaction with a slow reaction rate. ... The halogens or halogen elements are a series of nonmetal elements from Group 17 (old-style: VII or VIIA; Group 7 IUPAC Style) of the periodic table, comprising fluorine, F, chlorine, Cl, bromine, Br, iodine, I, and astatine, At. ... An iodide ion is an iodine atom with a −1 (negative one) charge. ... A bromide is a phrase, or person who uses phrases, which have been used and repeated so many times as to become either insincere in their meaning, or seem like an attempt at trying to explain the obvious. ... Acids and bases: Acid-base reaction theories pH Self-ionization of water Buffer solutions Systematic naming Electrochemistry Acid-base extraction Acids: Strong acids Weak acids Mineral acids Organic acids Bases: Strong bases Weak bases Organic bases edit In chemistry, a base is most commonly thought of as a substance that... In chemistry, nucleophilic substitution is a class of substitution reaction in which an electron-rich nucleophile attacks a molecule and replaces a group or atom, called the leaving group. ... The SN2 reaction is a type of nucleophilic substitution, where a nucleophile attacks an electrophilic center and bonds to it, expelling another group called a leaving group. ... The SN1 reaction is an substitution reaction in organic chemistry. ...

• steric hindrance increases
• basicity increases
• temperature increases
• the steric bulk of the base increases for example Potassium tert-butoxide
• the nucleophile is poor

In one study ^[1] the kinetic isotope effect (KIE) was determined for the gas phase reaction of several alkyl halides with the chlorate ion. In accordance with a E2 elimination the reaction with t-butyl chloride results in a KIE of 2.3. The methyl chloride reaction (only S_N2 possible) on the other hand has a KIE of 0.85 consistent with a S_N2 reaction because in this reaction type the C-H bonds tighten in the transition state. The KIE's for the ethyl (0.99) and isopropyl (1.72) analogues suggest competition between the two reaction modes. Steric effects are the interaction of molecules dictated by their shape and/or spatial relationships. ... Fig. ... An alkoxide is the conjugate base of an alcohol, and therefore has an organic group bonded to a negatively charged oxygen atom. ... In chemistry, a nucleophile (literally nucleus lover) is a reagent which is attracted to centres of positive charge. ... The kinetic isotope effect (KIE) is a variation in the reaction rate of a chemical reaction when an atom in one of the reactants is replaced by one of its isotopes. ... Definition The chlorate ion ClO3-. A chlorate (compound) is a compound that contains this group, with chlorine in oxidation state +5. ... ... Chloromethane or Methyl chloride is a chemical compound once widely used as a refrigerant. ...

Specific elimination reactions

The E1cB elimination reaction is a special type of elimination reaction involving carbanions. The E1cB reaction mechanism The E1cB elimination reaction is a special type of elimination reaction in organic chemistry. ...

In each of these elimination reactions the reactants have specific leaving groups: A leaving group is an atom or molecule that detaches from an organic molecule, which, after detachment, is called the residual or main part. ...

• the dehydration reaction is one where the leaving group is water.
• the Bamford-Stevens reaction with a tosyl hydrazone leaving group assisted by alkoxide
• the Cope reaction with an amine oxide leaving group
• the Hofmann elimination with quaternary amine leaving group
• the Chugaev reaction with a methyl xanthate leaving group
• the Grieco elimination with a selenoxide leaving group
• the Shapiro reaction with a tosyl hydrazone leaving group assisted by alkyllithium
• Hydrazone iodination with a hydrazone leaving group assisted by iodine
• A Grob fragmentation with degree of unsaturation increasing in one of the leaving groups.
• the Kornblum–DeLaMare rearrangement (elimination over a (H)C-O(OR) bond) with an alcohol leaving group forming a ketone

In chemistry, a dehydration reaction is a chemical reaction that involves the loss of water from the reacting molecule. ... The Bamford-Stevens reaction is a chemical reaction whereby treatment of tosylhydrazones with strong base gives alkenes. ... It has been suggested that this article or section be merged into Cope rearrangement. ... Hofmann elimination provides the dealkylation of quaternary ammonium salts to tertiary amines due to the scheme: quaternary ammonium salt via 1. ... The Chugaev elimination is a chemical reaction that involves the elimination of water from primary alcohols to produce terminal alkenes. ... The Grieco elimination is an organic reaction describing the elimination reaction of an aliphatic primary alcohol through a selenide to a terminal alkene . ... The Shapiro reaction or tosylhydrazone decomposition is an organic reaction in which a ketone or aldehyde is converted to an alkene through an intermediate hydrazone in the presence of 2 equivalents of strong base. ... Hydrazone iodination is an organic reaction in which a hydrazone is converted in a vinyl iodide by reaction of iodine and a non-nucleophilic base such as DBU . First published by D. H. R. Barton in 1962 the reaction is sometimes referred to as the Barton reaction (although one of... A Grob fragmentation is an elimination reaction taking place when an electrofuge and nucleofuge are situated in positions 1 and 3 on an aliphatic chain [1]. The reaction product is an electrofugal fragment (carbonium ion, acylium ion), an unsaturated fragment (alkene, alkyne, imine) and a nucleofugal fragment (leaving group such... The Kornblum–DeLaMare rearrangement is a rearrangement reaction in organic chemistry in which a primary or secondary organic peroxide is converted to the corresponding ketone and alcohol under base catalysis. ...

See also

• Important publications in organic chemistry

This is a list of important publications in chemistry, organized by field. ...

References

1. ^ Deuterium Kinetic Isotope Effects in Gas-Phase SN2 and E2 Reactions: Comparison of Experiment and Theory Stephanie M. Villano, Shuji Kato, and Veronica M. Bierbaum J. Am. Chem. Soc.; 2006; 128(3) pp 736 - 737; DOI abstract