Question

Which of the following statement is incorrect for bimolecular nucleophilic substitution reaction $\left(S{N}_2\right)$ ?

• A. In $S_{N}2$ reaction the substrate does not undergo heterolytic fission
• B. It is a second order reaction
• C. The rate of $S_{N}2$ reaction does not depend on concentrations of both substrate and nucleophilic reagent
• D. $S_{N}2$ reaction occurs in single step without forming intermediate

Answer 1

The correct option is C The rate of $S_{N}2$ reaction does not depend on concentrations of both substrate and nucleophilic reagent

$S_{N}2$ stands for bimolecular nucleophilic substitution reactions. This reaction takes place in a single step with the formation of intermediate transition state as follows:

$\underset{Substrate}{R-X}+\underset{Nucteophile}{O{H}^{-}}\to \underset{Transitionstate}{HO...R...X....}\to HO-R+X^{-}$

Since, both the substrate and the nucleophile take part in the rate-determining step, i.e., rate depends on the concentration of both, so the order of such reactions is 2. Here, the substrate does not undergo heterolytic fission.