In a $\mathrm{S}_{\mathrm{N}} 2$ substitution reaction of the type $\mathrm{R}-\mathrm{Br}+\mathrm{Cl}^{-}…

In a $\mathrm{S}_{\mathrm{N}} 2$ substitution reaction of the type $\mathrm{R}-\mathrm{Br}+\mathrm{Cl}^{-} \stackrel{\mathrm{DMF}}{\longrightarrow} \mathrm{R}-\mathrm{Cl}+\mathrm{Br}^{-}$ which one of the following has the highest relative rate?
  1. $\mathrm{CH}_{3}-\mathrm{CH}_{2}-\mathrm{CH}_{2} \mathrm{Br}$
  4. $\mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{Br}$

Solution

$\mathrm{S}_{\mathrm{N}} 2$ mechanism is followed in case of primary and secondary halides i.e., $\mathrm{S}_{\mathrm{N}}^{2}$ reaction is favoured by small groups on the carbon atom attached to halogens so

Asked in: BITSAT 2013

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