# How can an α,β-unsaturated ketone tautomerise?

I was taught that for aldehydes and ketone to exhibit keto-enol tautomerism, it is essential that there must be at least one α-hydrogen.

For example, acetophenone and butan-2-one show keto-enol tautomerism, but benzaldehyde and benzophenone don't show keto-enol tautomerism, since they don't have any α-hydrogens.

However, I was subsequently told that the cyclic enone 6,6-dimethylcyclohex-2-en-1-one also exhibits tautomerism:

How is this possible? It does not have any α-hydrogens (the vinylic proton cannot be enolised as it is orthogonal to the C=O π* orbital).

If you have an α,β-double bond next to your carbonyl, a γ hydrogen can also take part in tautomerism. Take crotonaldehyde $$\ce{H3C-CH=CH-CHO}$$:
$$\ce{O=CH-CH=CH-CH3 <<=> HO-CH=CH-CH=CH2}$$