Why is the #C_6H_8# molecule different from benzene with respect to resonance?
Benzene has two important equivalent resonance contributors, while any other
There are many molecules with the formula
Benzene has two equivalent resonance contributors, neither of which involves the separation of charge.
Hexa-1,3,5-triene has only one important resonance contributor.
Any other contributor we might draw has a separation of charge. For example,
Cyclohexa-1,3-diene is an "almost"-benzene.
But it is still a "linear" diene.
Like hexa-1,3,5-triene, it has only one important resonance contributor, with any other contributors having separation of charge.