Geometric requirements for the photolysis of aryloxiranes and cyclic carbonate esters

The photolysis of trans-β-methylstyrene oxide proceeds smoothly, but neither the corresponding cis-isomer nor β,β-dimethylstyrene oxide are photochemically active. Moreover, although styrene glycol carbonate undergoes photolysis to extrude carbon dioxide, the β,β-dimethylstyrene glycol carbonate is photochemically unreactive. These results are explained by looking at the energies required to obtain a conformation in which the plane of the aromatic ring is orthogonal to the orbitals of the epoxide moiety.