Photo-Claisen rearrangements of benzyl phenyl ether and benzyl l-naphthyl ether have been examined in cation-exchanged Y zeolites and polyethylenes of differing crystallinities. Ratios of the principal rearrangement products, benzyl arylol positional isomers, indicate that the reactions are more selective in the zeolites than in the polyethylenes. The results are explained on the basis of the active and passive walls of the reaction cages of zeolites and polyethylenes, respectively, and the limited free volume of the polyethylene cages.