The structure of benzene originally described by August Kekulé is shown below.

Explain, giving two different pieces of evidence, why this is not a valid structure for the bonding in benzene.

all (C–C) bond lengths equal / C–C bond lengths intermediate between C–C and C=C;

benzene normally undergoes substitution not addition;

thermochemically more stable than predicted / produces less heat when hydrogenated/combusted than predicted;

This part was generally well answered by many candidates.