Single-pulse shock tube kinetic studies of the thermal isomerizations of gaseous cycloheptene (CHEP) and cis-cyclooctene (COCT), and static reactor isomerizations of COCT at lower temperatures, have revealed a mechanistic dissimilarity in the two superficially analogous cycloalkene to, a,w-alkadiene reactions observed.At 1035-1256 K, CHEP produced mostly vinylcyclopentane, loglo(k,s-') = 15.1 (k 0.7) -69.7 (k 3.3) x 103/4.576T, and some 1,6-heptadiene. From COCT, heated over the range 610-1091 K, the dominant product was 1,7-octadiene, log& s-l) = 13.8 (k 0.2) -54.6 (k 0.5) x 103/4.576T, with small amounts of vinylcyclohexane formed at the higher temperatures, loglo(k, s-I) = 15.2 (& 0.3) -64.4 (k 1.2) x lo3/ 4.576T. The activation energy for the COCT isomerization to 1,7-octadiene is too low to associate with formation of a diradical, but is consistent with a concerted retro-ene mechanism. The higher activation energy isomerization to vinylcyclohexane, however, passes through a diradical transition structure. In contrast, the structure of CHEP is not adaptable to a concerted retro-ene process, and both 1,6-heptadiene and vinylcyclopentane are formed through diradical-mediated reactions.
ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.