Methylene radical reaction with cis ‐butene‐2

A study of the pressure dependence of the C 5 products from the reaction of cis ‐butene‐2 and methylene is reported. Methylene was produced by the photolysis of diazomethane with 4358 Å light at 23° or 56°, and by photolysis of ketene with 3200 Å radiation at 23° or 100°. The change with increasing pressure of the relative amounts of the characteristically “triplet products” ( trans ‐1,2‐dimethylcyclopropane, trans ‐pentene‐2 (TP2), and 3‐methylbutene‐1 (3MB1)) and “singlet products” ( cis ‐1,2‐dimethylcyclopropane (CDMC) and cis ‐pentene‐2 (CP2)) are discussed. The behavior is reminiscent of that found in 3 CH 2 ‐ cis ‐butene‐2 systems and can be interpreted in terms of the rapid rate of rearrangement of an initial triplet diradical product component, due to 3 CH 2 , relative to the slower rate and readier collisional stabilization of an initial vibrationally‐excited dimethyl cyclopropane product component, due to 1 CH 2 . Relative rates of reactions of 1 CH 2 with allylic CH:vinyl CH:CC in the neat liquid were, for diazomethane, 1:1.1:7.2 and, for ketene, 1:1.2:6.7.