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(a) Give a detailed account on the different mechanisms followed in elimination reaction. |
Answer» Solution :(a) Elimination reactions MAY proceed through two different mechanisms namely `E_(1) and E_(2)`  (i) The rat of `E_(2)` reaction depends on the concentration of alkyl halide and base Rate =K [alkyl halide] [base] (ii) It is therefore , a SECOND order reaction. Generally primary alkyl halide UNDERGOES this reaction in the presence of alcoholic KOH. It is a one step process in which the abstraction of the proton from the `beta` carbon and expulsion of halide from the `alpha` carbon occur simultaneously. The mechanism is shown below.  (iii) Generally, TERTIARY alkyl halide which undergoes elimination reaction by this mechanism in the presence of alcoholic KOH. It follows first order kinetics . Let us consider the following elimination. Step-1 : Heterolytic FISSION to yield a carbocation  Step-2 : Elimination of a proton from the `beta` - carbon to produce an alkene. 
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