Question

Draw the radical bromination mechanism of isopropyl benzene. Show all electron flow with arrows and all intermediate structures.

a) Initiation step
b) Propagation step
c) Termination step
d) Substitution step

Answer 1

a) Initiation: Light breaks into bromine radicals.

b) Propagation: Cumyl radical forms from isopropyl benzene, reacts with

Br₂, forming cumyl bromide.

c) Termination: Bromine radicals combine to form Br₂.

d) Substitution: Cumyl bromide may further react in varied ways depending on conditions.

Step-by-step explanation:

Initiation step:

In the presence of light or heat, the bromine molecule (Br) is homolytically cleaved to form two bromine radicals (2Br•).

Propagation step:

The bromine radical reacts with isopropylbenzene (C₆H₅CH(CH₃)₂) to form a benzylic radical, which then reacts with Br₂ to form a brominated product and a bromine radical.

This process can repeat multiple times, resulting in the substitution of several bromine atoms.

Termination step:

Two bromine radicals combine to form a non-reactive species, effectively terminating the chain reaction.

Substitution step:

The bromine radicals react with the aromatic ring of isopropylbenzene, resulting in the substitution of a hydrogen atom with a bromine atom.