43bE - Organic Chemistry (Mcmurry)

Question

What effect would you expect the following changes to have on the rate of the reaction of 1-iodo-2-methylbutane with cyanide ion? 

(b) Both the  and the 1-iodo-2-methylbutane concentrations are tripled.

    

Step-by-Step Solution

Answer

S N 2 reaction

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

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

 

 

 

Rate of the reaction

In  $S_{N}2$ rate of the reaction depend on the reacting species and nucleophile.

Hence, triple the concentration of cyanide ion and the concentration of 1iodo2methyl butane. The net rate of the reaction becomes nine-foldandincreases by nine times. Hence, the reaction becomes very fast.

$\begin{array}{c}R\text{\hspace{0.33em}}=K\left(R.S\right)\left(N\right)\\ =K\left(3\right)\left(3\right)\\ =9K\end{array}$