The photochemistry in methanol of the esters 12 ad has been studied in order to determine the importance of internal return of both ion pair and radical pair intermediates. The efficiency of internal return, determined by monitoring 18O exchange between the alcohol and carbonyl oxygens, was shown to be substituent dependent, varying from approximately 10% for the 4, 7-dimethoxy substrate to nearly 50% for the 4-cyano case. The ...
