Problems Associated with Distinguishing between Singlet Oxygen and Electron Transfer Photooxygenation Reactions

In the introduction a review is given of the various methods available for probing the mechanism of photooxygenation reactions. To illustrate the methodology, some new results on the photooxygenation of alpha-ketocarboxylic acids and esters is given in which it is shown that these compounds sensitise singlet oxygen formation but are relatively unreactive to this oxidising species. Alternative mechanistic schemes are proposed.