Question

How can Polyhalogenation be prevented?

Answer 1

Answer:

In order to avoid polyhalogenation the reactions are usually carried out under conditions of excess alkane. In those circumstances the halogen is much less likely to react with the more reactive mono-halogenated product because it will be formed in tiny amount compared to the amount of starting alkane.

Answer 2

Bromination of alkanes occurs by a similar mechanism, but is slower and more selective because a bromine atom is a less reactive hydrogen abstraction agent than a chlorine atom.