Hydrogenation energy of cyclohexene is -120kJmol-1 while that of benzene is-208 kJmol-1. Explain this observation. ? ?

The difference in hydrogenation energy between cyclohexene and benzene can be attributed to the difference in their molecular structures.

Cyclohexene is a cyclic compound with a double bond, while benzene is a cyclic compound with alternating double bonds. The presence of double bonds in the molecules affects the stability and energy required for hydrogenation.

In the case of cyclohexene, the double bond can easily be broken to allow for the addition of hydrogen atoms, resulting in a lower hydrogenation energy of -120 kJmol-1. On the other hand, benzene has a more stable aromatic ring structure with delocalized pi electrons, making it more difficult to break the double bonds and add hydrogen atoms. This results in a higher hydrogenation energy of -208 kJmol-1 for benzene.

Overall, the difference in hydrogenation energy between cyclohexene and benzene can be explained by the difference in their molecular structures and the stability of their double bonds.