Thermolysis of 1,2-Dioxetanes: Activation Parameters and Chemiexcitation Yields for Unsymmetric Cis/Trans Isomers

Article abstract of DOI:10.1021/jo00391a024

Fifteen unsymmetrically substituted dioxetanes were synthesized and characterized.The activation parameters for thermolysis of series I in xylenes showed the cis compound (R = phenyl) to be more stable than the trans isomer.As the R group (series I) increased in steric bulk, the stability difference between cis/trans pairs was in qualitative agreement with that above but was well within experimental error such that the isomers must be regarded as being of equal stability.For series II, the trans-dialkyldioxetane was more stable than the cis compound, in agreement with group additivity type calculations based on the diradical mechanism of dioxetane thermolysis and the results for cis/trans symmetric dioxetanes with "large" substituents.Recent work by Adam on cis/trans-3,4-dimethyl-1,2-dioxetanes had shown that the cis compound was more stable than the trans isomer.The present data for series I and II suggest that there is a smooth transition in behavior between the two extreme cases.The results are interpreted in relation to dioxetane strusture and the mechanism of thermolysis.Chemiexcitation yields for the 15 compounds are reported.