Question

For a certain substitution reaction, the rate of substitution is found to be independent of both the concentration and the nature of the nucleophile. What is the most likely mechanism?

For a certain substitution reaction, the rate of substitution is found to be independent of both the concentration and the nature of the nucleophile. What is the most likely mechanism?

Answer 1

Concepts and reason

The correct option needs to be chosen amongst the given set of mechanisms in which the concentration of nucleophile has no effect on the reaction rate.

Consider the mechanism of each reaction and determine the reaction rate from the slow step.

Fundamentals

${{\rm{S}}_{\rm{N}}}1$ reaction: It stands for substitution nucleophilic unimolecular reaction. The reaction is a two-step reaction. The first step involves the removal of halide ion to form carbocation. The attack of nucleophile occurs in the second step.

${{\rm{S}}_{\rm{N}}}2$ reaction: It stands for substitution nucleophilic bimolecular reaction. The reaction is a single step and the removal of halide ion and the attack of the incoming nucleophile occurs in the same step.

The rate of ${{\rm{S}}_{\rm{N}}}1$ reaction is dependent on the concentration of the haloalkane and the concentration of nucleophile has no effect on reaction rate.

The rate of ${{\rm{S}}_{\rm{N}}}2$ reaction is dependent on the concentration of the haloalkane as well as the nucleophile.

Ans:

Choose the correct options as follows: