Photochemistry of Substituted Methyl a-Arylcinnamates: Ortho and Para-Substitution.

Christopher H. Evans a)*, Jóhannes Reynissona,b), Jón K.F. Geirsson a), Ágúst Kvaran a) and W.G. McGimpsey b)

a) Science Institute, University of Iceland, Dunhaga 3, IS-107 Reykjavik, Iceland.

b) Department of Chemistry and Biochemistry, Worcester Polytechnic Institute, 100 Institute Rd., Worcester, MA 01609-2280, USA.

* Author to whom correspondence should be addressed.


The 308 nm laser photochemistry of a series of substituted methyl a-arylcinnamates has been studied in deoxygenated hexane and acetonitrile. Methyl a-phenylcinnamate (1a) and derivatives that are p-substituted with electron withdrawing (chloro ,1b) or electron donating (methoxy, 1c) groups exhibited very similar photochemistry and spectroscopic 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 (1d) was found to be only 0.5. This difference is discussed in terms of possible influences of the o,o-dichloro substituents on the excited state potential energy surface for arylcinnamate photoisomerization.