Explain dehydrohalogenation (`beta` - elimination) of alkyl halides.

Explanation

When a haloalkane with `beta` - hydrogen atom is heated with alcoholic solution of potassium hydroxide, there is elimination of hydrogen atom from `beta` - carbon and a halogen atom from the `alpha` - carbon atom. As a result, an alkene is formed as a product.
Since `beta` - hydrogen atom is formed as a product.
Since `beta` - hydrogen atom is involved in elimination, it is often called `beta` - elimination.
If there is possibility of formation of more than one alkene due to the availability of more than one `beta` - hydrogen atoms, usually one alkene is formed as the major product.

These form part of a pattern first observed by Russian chemist, ..Alexander Zaitsev... He formulated rule which can be summarised as :
..In dehydrohalogenation reactions, the preferred product is that alkene which has greater number of alkyl groups attached to doubly bonded carbon atoms... Thus, 2-bromopentane gives pent-2-ene as the major product.