question_answer

Which one of the following alkenes will react faster with Ha under catalytic hydrogenation conditions? (R = Alkyl Substituent)

A)

B)

C)

D)

Correct Answer: A

Solution :

 Heat of hydrogenation of alkene\[\propto \frac{\text{1}}{\text{Stability}\,\text{of}\,\text{alkene}}\] Hence the alkene which will react fastest with \[{{H}_{2}}\]will be the least stable. Among the given options the compound having least number of alkyl groups (R) will be the least stable. Further the relative rates of hydrogenation decrease with increase of steric hindrance Hencewill react fast with \[{{H}_{2}}.\]