Question

Why is halogenation important?

Answer 1

Because it introduces functionality onto a carbon chain (sometimes selectively), that can be further elaborated.

Explanation:

Hydrocarbons, the ones we pump from the ground, are rather unreactive molecules. Of course you can burn them (and we do to supply energy!), but other than that they are rather inert.

Radical halogenation (or hydrohalogenation of olefins) allows the introduction of an halide group at a predictable position on the carbon chain. This `C-X` can be hydrolyzed to give alcohols, the which can be further oxidized to give ketones and aldehydes and acids. Of course `C-X` can be eliminated to give olefins, or substituted by amines to give nitrogen containing species. So in short, halogenation offers opportunities for reactivity and elaboration of products.