Reactions of triplet methylene radicals with alkanes

Abstract

Studies have been made of the products resulting from reaction between triplet methylene and several alkanes, propane, n-butane, and isobutane. Triplet methylene was produced by photolysis of diazomethane in the presence of a large excess of inert nitrogen gas. Complicating side reactions involving diazomethane were encountered.Observation of higher products allowed the determination of the relative rates of 1°:2°:3° H abstraction from C—H bonds; these are ~1:14:150. The rate of addition of 3CH2 to the C=C bond in ethylene appears to proceed ~ 3.5 times faster than H abstraction from a 3 °C—H bond. The possible occurrence of insertion by 3CH2 into C—H bonds is discussed and relative rates of insertion for 1°:2°:3° bonds are deduced to be ~ 1:2:7. Comparisons of the relative rates of insertion abstraction are also given. Studies with propane-d6 indicated an isotope effect for abstraction of H:D from the 1 position of ~ 3.9; insertion by 3CH2 into the same position showed an isotope effect of ~ 2.