The major product of the free radical halogenation of alkane A with N-bromosuccinimide is the corresponding tertiary bromide.
The free radical halogenation of alkanes using N-bromosuccinimide (NBS) typically involves the abstraction of a hydrogen atom by a bromine radical.
The resulting alkyl radical can then react with NBS to form the brominated alkane.
However, NBS is selective in the bromination process and tends to preferentially brominate tertiary carbon atoms over primary or secondary carbons.
This selectivity is due to the stability of the resulting tertiary radicals.
Let's take an example alkane, propane (CH3-CH2-CH3), and consider the major product formed through free radical bromination using NBS.
The reaction proceeds through a radical chain mechanism:
Initiation:
NBS generates bromine radicals (Br·) in the presence of a radical initiator, such as benzoyl peroxide (BPO).
Br2 + NBS → Br· + NBS-Br·
Propagation: Br· attacks a carbon atom in alkane A, forming a 2° alkyl radical.
R-H + Br· → R· + HBr
Termination: Alkyl radicals react with Br· to form bromoalkanes.
R· + Br· → R-Br