| Abstract
| - Kinetic studies of the thermal isomerization and fragmentation reactions exhibited by cis- andtrans-1-(E)-propenyl-2-methylcyclobutanes at 275 °C in the gas phase have provided first-orderrate constants for cis,trans interconversions of the cyclobutanes, 1,3-carbon migrations leading to3,4- and 3,6-dimethylcyclohexenes, isomerizations providing directly and indirectly four acyclicdienes, and fragmentations to ethylene, propene, and mixtures of pentadienes and hexadienes.Both cis and trans isomers of 1-(E)-propenyl-2-methylcyclobutane form trans-3,4-dimethylcyclohexene faster than they are converted to cis-3,4-dimethylcyclohexene; the trans reactant gives riseto cis-3,6-dimethylcyclohexene in preference to its trans isomer, while the cis starting materialgives neither at measurable rates; both form the relatively minor product 1,6-(Z)-octadiene. Therate constants derived from 35 kinetic runs starting with four distinct 1-(E)-propenyl-2-methylcyclobutane samples are consistent to within narrow error limits. The stereomutations, isomerizations,and fragmentations of the 1-(E)-propenyl-2-methylcyclobutanes are interpreted in terms ofcompetitive processes involving conformationally flexible short-lived 2-(E)-octene-4,7-diyl and3-methyl-5-(E)-heptene-1,4-diyl diradicals.
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