Liquid-crystalline solvents as mechanistic probes. 23. norrish II reactions of 2- and sym-alkanones in the isotropic, smectic B, and crystallin

n -Alkanones with the carbonyl group at the 2 or central positions ( 1 and 2 , respectively) have been irradiated in the isotropic, smectic B, and two solid phases of n -butyl stearate ( BS ). The lengths of the ketones were varied from 11 to 31 carbons. The ratios of elimination/cyclization products and diastereomeric cyclobutanol products were measured for each as a function of temperature and BS phase. The effect of 1 and 2 on the phase transition temperatures of BS has been correlated with changes in the product ratios. The experiments demonstrate that a very sensitive cooperative relationship exists between the ease with which 1 and 2 fit into the ordered phases of BS and the degree to which the solvent matrices influence ketone photochemistry. The influence of solvent order on the product ratios is distinctly different for 1 and 2 , and for the two product ratios from one ketone.