Question

The heat of hydrogenation of an unsaturated compound can be used to estimate its stability. The heat of hydrogenation of benzene is _____ than expected by comparison with cyclohexene and 1,3-cyclohexadiene. This difference indicates that benzene is much _____ stable than a system containing three isolated double bonds.

Answer 1

Answer: The heat of hydrogenation of benzene is lower

Explanation: less, lower (since benzene is more stable than expected, it is already at a lower energy than an isolated triene. Less energy will therefore be released during hydrogenation).

Answer: This means that real benzene is about 150 kJ mol -1 more stable than the Kekulé structure gives it credit for. This increase in stability of benzene is known as the delocalization energy or resonance energy of benzene.