Liquid Crystalline Solvents as Mechanistic Probes. IV. The Influence of Ordered Media on the Norrish Type II Photoprocesses in α‐Diketones

The Norrish II photoreactions of octane‐4,5‐dione (1) and 1,6‐diphenylhexane‐3,4‐dione (2) have been investigated at several temperatures and in isotropic and ordered (liquid crystalline) media. The sole photoproducts detected in all solvents are 1/1 diastereomeric mixtures of α‐hydroxycyclobutanones. The quantum yields for disappearance of 1 and 2 tend to decrease as the temperature increases in all media investigated. Whereas the quantum yield ratio for disappearance of 1 in cholesteric mesophases and hexane is greater than one, the ratio for disappearance of 2 is less than one. Possible explanations for these observations, based upon the influence of solvent order on solute conformational lability, are advanced.