Allylic and Benzylic substitution

Added: 2026-05-16

[00:00:00]Hello students. Let us study about allylic and benzylic substitution. Which is free radical substitution which happens in presence of chlorine or bromine at high temperature or sunlight. Even you can use NCS and NBS, N-bromosuccinimide.

[00:00:16]Okay. Whenever you take chlorine in presence of sunlight or heat or NCS, chlorine free radical it gives.

[00:00:23]Bromine sunlight or heat it gives bromine free radical.

[00:00:26]Okay. Let us know Let us study the reactions.

[00:00:30]Here double bonded next sp3 carbon is called as This is allylic carbon.

[00:00:36]Okay, now. And benzene ring next sp3 carbon is called as benzylic carbon.

[00:00:42]Whenever you take sunlight, okay, and chlorine here hydrogen is replaced by from allylic position hydrogen is replaced by chlorine.

[00:00:51]Got it.

[00:00:52]And whenever you take bromine and UV light or high temperature, from benzylic carbon hydrogen is replaced by bromine.

[00:01:00]Replaced by bromine.

[00:01:04]So here, whenever it treated with chlorine in presence of sunlight, this is allylic carbon, this is also allylic carbon.

[00:01:12]Here hydrogen is replaced by chlorine.