Which of the following is correct?

Options

A. Alkynes are more reactive than alkenes toward catalytic hydrogenation.
B. the hydrohenation of alkynes is more exothermic than the hydrogentation of alkenes
C. both alkynes and alkenes are equally reactive toward catalytic hydrogentationl.
D. both (1) and (2)

Answer

D

Explanation

Alkenes are adsorbed on the surface of the catalyst only when the plane of the `pi` bond approaches head on (perpendicularly). Because of the cylindrical nature of the `pi` bonds of alkynes, any approach along the axis of the cylinder is successful. These less constrained transition states cause alkynes to have more positive `DeltaS` values. Consequently, alkynes react faster than alkenes.