STEREOSELECTIVITY REVERSAL OF A PHOTOCHEMICAL REACTION IN THE SOLID STATE

Article abstract of DOI:10.1016/S0040-4039(00)98257-1

The stereoselectivity of Norrish type II cyclobutanol formation resulting from photolysis of α-adamantyl-p-methoxyacetophenone is altered in favor of the more hindered cis isomer as the reaction medium is changed from isotropic liquid phases (benzene or acetonitrile) to the pure crystal.Based on the reactant X-ray crystal structure, it is suggested that the intermediate 1,4-biradical in the solid state is born in, and restricted to, a conformation which is ideal for direct closure to the more hindered product.In the relatively unrestricted solution environment, however, conformational isomerism of the biradical is faster than closure, thus leading to a predominance of the less hindered trans cyclobutanol.