Inverse temperature dependence of the dipolarophilic reactivity of carbonyl ylide photogenerated from trans-stilbene oxide

Abstract

In methylcyclohexane at 295 – 353 K, cycloaddition reactions of carbonyl ylide photogenerated from trans-stilbene oxide have small or negative activation enthalpies. This behavior can be explained in terms of reversible formation of a bimolecular complex. The increase in reactivity from one dipolarophile to another is due to the increase in differential activation entropy for collapse and back-dissociation of the complex.