Name: Conversion
Uploaded: 2019-07-19
Duration: 8 min 3 s
Description: Let's see how nucleophilic substitution takes place in a lab. How can you make it happen? Why does it happen? You'll learn and see and will be stunned beyond...

Question

Explain the mechanism of $S_{N} 2$ reaction with example.

Accepted Answer

$S_{N} 2$ reaction follows second order kinetics and the rate of reaction depends upon both haloalkane and participating nucleophile. Hence, this reaction is known as substitution nucleophilic bimolecular reaction. In this reaction, the nucleophile attacks the positively charged carbon and the halogen leaves the group. It is a one-step reaction. Both the formation of carbocation and exiting of halogen take place simultaneously.

So opposite to the $S_{N} 1$ reaction mechanism, this is favoured mostly by primary carbon, then secondary carbon and then tertiary carbon.

$S_{N} 2$ reaction of an optically active haloalkane is always accompanied by inversion of configuration at the asymmetric centre. Let us consider the following example:
When $2$ -Bromooctane is heated with sodium hydroxide, $2$ -octanol is formed with inversion of configuration. When ( $-$ )- $2$ -Bromo octane is heated with sodium hydroxide, ( $+$ )- $2$ -Octanol is formed, in which $- OH$ group occupies a position opposite to what bromine had occupied.

Where,

(a) = ( $-$ )- $2$ - Bromo octane
(b) = Transition State
(c) = ( $+$ )- $2$ -Octanol (product)

Embibe Experts Solutions for Chapter: Haloalkanes and Haloarenes, Exercise 1: Andhra Pradesh Board-2020

Embibe Experts Chemistry Solutions for Exercise - Embibe Experts Solutions for Chapter: Haloalkanes and Haloarenes, Exercise 1: Andhra Pradesh Board-2020

Questions from Embibe Experts Solutions for Chapter: Haloalkanes and Haloarenes, Exercise 1: Andhra Pradesh Board-2020 with Hints & Solutions

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