91Ó°ÊÓ

First-order nucleophilic substitution reaction (S_N1) comprises two steps. In the first step carbon halogen bond breaks to form a carbocation and in the second step nucleophile attacks the carbocation to form a new bond.

Because they form relatively stable carbocations, benzyl halides undergo S_N1 reaction more easily than do most alkyl halides.

Here, the dehalogenation of the bromine atom forms a carbocation.

The carbocation formed undergoes resonance to gain stability. The benzylic carbocation is the most stable among all the resonating carbocations.

The nucleophilic attack of the lone pair of oxygen to the empty p-orbital of benzylic carbon forms the final product.

The final product here seen is benzyl ethyl ether.