Question

Among alkyl halides order of reactivity of SN2 reaction is Ch3X 》p-RX 》sec-RX 》tert-RX. Discuss the factors which are mainly responsible for this order

Answer 1

Stereo hindrance, ie more strict hindrance less reactivity of sn2. As it is least in CH3X and highest in tertX , ch3x easily gives sn2 while others won't

Answer 2

Explanation:

$SN_{2}$ is a one step reaction. In this a transition state is formed.  Among alkyl halides order of reactivity of SN2 reaction is Ch3X > p-RX > sec-RX > tert-RX because the rate of reactivity is inversely proportional to the bulkiness of groups attached to the central carbon atom.

Therefore, more is the number of bulkier groups attached to the carbon, more will be the steric hindrance. Hence, nucleophile will find it difficult to attack the molecule. As a result, rate of reaction will decrease.

In case of $CH_{3}X$, only one atom X is attached to the $CH_{3}$ molecule therefore, there will be no steric hindrance. But as the number of atoms increases around carbon atom then steric hindrance will also increase. That is why, order of the rate of reaction is as follows. $CH_{3}$ > p-RX > sec-RX > tert-RX.