Photochemistry of Hydroxyaromatic Compounds
Although it is well known that phenols and hydroxyarenes are in general much stronger acids in the excited singlet state than in the ground or excited triplet state [1.2], the utility of this phenomenon for inducing new chemistry has not been c\tcnsivcly exploited. Much work continues in the study of the photoprototopic behavior of these compounds [3-5]. Of particular interest is intramolecular proton transfer, which may be rationalized as arising from the enhanced acidity of the phenolic (hydroxyarcnc) proton coupled with the enhanced basicity of another functional group on the same molecule. Such a broad topic is, however, beyond the scope of this chapter. Rather, the focus will be restricted to photochemical reactions of phenols and hydroxyarcncs that may be loosely interpreted as resulting from their enhanced acidity in the singlet excited state. An attempt will be made to he inclusive rather than exclusive. For example, if replacement of the phenolic group by mcthoxy results in significant reduction in reaction efficiency (or changes the reaction path), then it is probable that the photoreaction concerned will be covered.