PHOTOCHEMISTRY OF SUBSTITUTED METHYL-ALPHA-ARYLCINNAMATES - ORTHO-SUBSTITUTION AND PARA-SUBSTITUTION

The 308 nm laser photochemistry of a series of substituted methyl-alph a-arylcinnamates has been studied in deoxygenated hexane and acetonitr ile. Methyl-alpha-phenylcinnamate (1a) and derivatives that are p-subs tituted with electron withdrawing (chloro, Ib) or electron donating (m ethoxy, Ic) groups exhibited very similar photochemistry and spectrosc opic properties, with the photostationary state (pss) composition ([E] /[Z]) being. on the average, 2.8 for these substances. By contrast the pss value for the o,o-dichloro substituted arylcinnamate (Id) was fou nd to be only 0.5. This difference is discussed in terms of possible i nfluences of the o,o-dichloro substituents on the excited state potent ial energy surface for arylcinnamate photoisomerization. (C) 1998 Else vier Science S.A. All rights reserved.