Resonance stabilization energies from cis-trans isomerization studies. Comment

Abstract

In a recent publication,1 Marley and Jeffers reported single pulse shock tube relative rate measurements for the cis-trans isomerization of crotononitrile, 1,3-pentadiene, and 3-methyl-l,3-pentadiene. The results are log k (crotononitrile) = 13.2 -58.1/9, log k (1,3-pentadiene) = 13.6 -53.0/9, and log k (3-methyl-1,3-pentadiene) = 14.0 -55.0/9, where 9 = 2.303RT kcal/mol. On the assumption of a biradical mechanism for cis-trans isomerization the authors compared these findings with their previously methyl-1,3-pentadiene almost certainly proceeds via the intermediate formation of 1,2,3-trlmethylcyclobutane and not via a biradical mechanism. These workers also studied the cis-trans Isomerization of 1,3-pentadiene. The situation was less clear but again intermediate formation of a cyclobutane seemed more likely than a biradical mechanism. A similar pathway for 3-methyl-1,3-pentadiene seems likely. This paper was overlooked by Marley and Jeffers.