TRIPLET METHYLENE RADICAL REACTION WITH CIS-BUTENE-2

A study of the pressure dependence of the C5 products of the reaction between cis-butene-2 and triplet methylene radicals is reported. Triplet methylene was produced by collisional deactivation (in the presence of a large excess of nitrogen) of the methylene produced by the photolysis of diazomethane with 4358-A radiation at 23°, and with unfiltered light at 23 and 56°. Reaction pressures were varied from 0.3 to 3.5 atm; a constant ratio of cis-butene-2:diazomethane:nitrogen was maintained at 20:1:30,000. The observed pressure dependence of the product proportions indicates that alkene products arise, in part, by isomerization of the triplet dimethylcyclopropanes or diradicals, rather than exclusively by a concomitant noninterceptible formation reaction. There is a pressure dependence of the ratio of trans-:cis-dimethylcyclopropane which, together with the pressure variability of products such as 3-methylbutene-1, dictates caution in the interpretation of the proportions of 3CH2:1CH2 from product proportions in photolysis systems and provides an alternative interpretation of a previous finding of the authors.