Advices For Studying Organic Chemistry

Figure 13.1 The relative stability of the allyl radical compared to 1°, 2°, 3°, and
vinyl radicals. (The stabilities of the radicals are relative to the
hydrocarbon from which was formed, and the overall order of stability
is allyl > 3° > 2° > 1° > vinyl).
2) Relative stability of radicals:
allylic or allyl > 3° > 2° > 1° > vinyl or vinylic

13.2B ALLYLIC BROMINATION WITH N-BROMOSUCCINIMIDE

(LOW CONCENTRATION OF Br 2 )

1. Propene undergoes allylic bromination when treated with N-bromosuccinimide
   (NBS) in CCl 4 in the presence of peroxides or light.

CH 2 CH CH 3 N

O

O

O

O

+ Br CCl 4 CH 2 CH CH 2 Br

N-Bromosuccinimide

light or ROOR

3-Bromopropene

(NBS) (allyl bromide)

N H

Succinimide

+

1) The reaction is initiated by the formation of a small amount of Br•.

2) The main propagation steps: