46bE - Organic Chemistry (Mcmurry)

Question

Which reaction in each of the following pairs would you expect to be faster? 

(b) The  displacement by  on bromoethane or on bromocyclohexane

Step-by-Step Solution

Answer

Bromoethane $is\text{\hspace{0.33em}}showfastreactionthan$bromocyclohexane 

S N 2 reaction

It is a nucleophilic substitution reaction in which an old bond is broken, and a new bond is formed. Bothprocessesco-occur. Hence, it’s a single-step reaction.

The two reacting species are involved in the rate-determining steps.

 

Nucleophile

Nucleophiles are the negatively charged ions or the neutral species having the lone pair of electrons ready for bonding. 

Species react faster with C H 3 C O 2 -

If the species is a better leaving group, it reacts faster with the nucleophile.

Here, both the substrates are different. Bromoethane is a primary alkane,bromocyclohexane is a secondary alkane and $S_{N}2$ reaction is shown by primary alkane showing a single-step reaction.

Bromoethane is a better leaving group thanbromocyclohexane

Bromoethaneshows fast reaction than bromocyclohexane