Question

The heat of hydrogenation of cyclohexene is 28.6 kcal and that of cyclohexadiene is about twice as much (i.e, 55.4kcal). What then would be the heat of hydrogenation of benzene, which has three double bonds?

• A. Thrice that of cyclohexene (28.6 3 kcal)
• B. The same as that of cyclohexene
• C. The same as that of cyclohexadiene
• D. 49.8 kcal

Answer 1

The correct option is D 49.8 kcal

In benzene 3 double bonds are in $\pi$ cloud which has an only partial double bond as all electrons are in resonance.

Thus it requires lesser energy than 2 double bonds and more than 1 double bond.

Thus, Hydrogenation energy of Benzene is 49.8kcal