Steric and substituenteffects on the photochemical reaction of 2,4,6-trialkylphenyl ketones has been investigated. A striking steric effect was observed in the photoreaction of 2,4,6-trialkylbenzophenones. The more hindered the carbonyl group, the more readily photoenolization occurs resulting in intramolecular cyclization leading to benzocyclobutenol derivatives. With 2,4,6-trialkylacetophenones