what is elimination reaction explain with example
Answers
Elimination reactions are commonly known by the kind of atoms or groups of atoms leaving the molecule. The removal of a hydrogen atom and a halogen atom, for example, is known as dehydrohalogenation; when both leaving atoms are halogens, the reaction is known as dehalogenation.
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Explanation:
Elimination reactions are chemical reactions in which atoms or groups of atoms are removed from a molecule, resulting in the formation of a new double or triple bond. There are two types of elimination reactions: E1 and E2.
E1 Reaction:
In an E1 reaction, the substrate undergoes a unimolecular elimination (i.e., one molecule participates in the rate-determining step). In this reaction, a leaving group leaves the substrate to form a carbocation. The carbocation then rapidly loses a proton to form the alkene product.
Example:
The following reaction is an example of an E1 reaction. Here, tert-butanol is treated with concentrated sulfuric acid to form a carbocation, which then undergoes elimination of water to form the alkene:
CH3CH(OH)CH3 + H2SO4 → CH3C+(CH3)CH2 + HSO4-
CH3C+(CH3)CH2 → CH2=C(CH3)2 + H+
E2 Reaction:
In an E2 reaction, the substrate undergoes a bimolecular elimination (i.e., two molecules participate in the rate-determining step). In this reaction, the leaving group leaves the substrate simultaneously with the removal of a proton by a base, resulting in the formation of the alkene product.
Example:
The following reaction is an example of an E2 reaction. In this case, 2-bromo-2-methylpropane is treated with sodium ethoxide (NaOEt) in ethanol solvent to form ethene:
(CH3)3C-Br + NaOEt → (CH3)2C=CH2 + NaBr + EtOH