Question

What do the pathway and stoichiometry of halogenation depend on?

Answer 1

The main concern is with the degree of the `alpha` carbon.

A tertiary radical in the propagation step is more stable than a primary radical due to hyperconjugation.

Another concern is energy to homolytically cleave the diatomic halogen molecule. Without heat or light, the reaction won't happen at an appreciable rate.

Moreover, halogen radicals that are reactive to a common degree are `Br` and `Cl`. Chlorination is less selective than bromination, and bromination is used to avoid primary halogenation.