Question

Draw the alkene formed when 1-heptyne is treated with one equivalent of HBr.

Answer 1

Concepts and reason

Hydrohalogenation reaction: Alkynes undergo a reaction with hydrogen halide and form a halogenated alkene as a product. The addition of hydrogen and halogen to alkene follows the Markonikov’s addition.

Markonikov’s addition: In the addition of hydrogen halide to alkene or alkyne, the hydrogen in hydrogen halide will form a bond to carbon atom that contains more hydrogen atoms in the starting alkene or alkyne.

Fundamentals

Example for hydrohalogenation reaction of alkynes:

The triple bond in alkyne abstracts hydrogen from hydrogen halide and forms a carbocation, then chlorine atom attacks carbocation and forms halogenated alkene. This reaction follows the Markonikov’s rule.

Structure of 1 – heptyne:

Ans: