NORRISH-II REACTIONS OF LIQUID-CRYSTALLINE KETONES - COMPARISON BETWEEN SMECTIC-B AND SOLID-PHASE ORDER AND CONTROL OF PHOTOPRODUCT DISTRIBUTIONS

The Norrish II photoreactions of trans-1-(4-heptanoylphenyl)-4-heptylcyclohexane (2a) and trans-1-heptyl-(4-(4-nonanoylphenyl)cyclohexane (2b) have been examined in their isotropic, smectic B, and solid phases. The smectic phases have been characterized by optical microscopy, differential scanning calorimetry, and X-ray diffraction. Solid and smectic phase order, probed by deuterium NMR spectroscopy of 2 deuteriated at the methylene-alpha to the carbonyl group, is correlated with the photochemical results. The apparent absence of a directing influence of the smectic B phases on the course of the Norrish II reactions of 2 is attributed to the local fluidity afforded the methylene groups of thc alkyl chains. The solid phase influence on the distribution of Norrish 11 photoproducts is significant and indicates that a small amount of motional freedom persists in the alkyl chains even after bulk crystallization.