Question

Explain with a mechanism why the reaction of 2-pentyne with HCl produces 2,2-dichloropentane and 3,3-dichloropentane, but not 2,3-dichloropentane.

Answer 1

Addition of HCl to carbon-carbon multiple bond follows Markovnikov's rule, which states that addition of negative part of the reagent occurs at that carbon which contains lowest number of hydrogen atoms.

Reaction of 2-Pentyne with HCl takes place as follows:

Since, the reaction occurs according to the Markovnikov's rule therefore, the formation of 2,3-dichlorochloro does not occurs.