Which of the following dienes undergoes the least exothermic hydrogenation upon treatment with `H_2`/Pd

Options

A. 2
B. 4
C. 3
D. 1

Answer

D

Explanation

The enhanced stability of a conjugated diene compared to a non-conjugated diene imparts it with a lower heat of hydrogenation (this is only valid when the alkenes being compared undergo hydrogenation to give the same alkane). This is the only conjugated diene shown