1.

Explain dehydrohalogenation (beta - elimination) of alkyl halides.

Answer»

Solution :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.


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