PICOSECOND RADICAL KINETICS - BOND-CLEAVAGE OF THE CUBYLCARBINYL RADICAL

Rate constants for the initial bond cleavages of the cubylcarbinyl radical (1) were determined by competition kinetics using benzeneselenol as a trapping agent. Measurements over the temperature range -78 to 25-degrees-C gave a temperature-dependent function of log (k(r).s) = 13.16 - 3.72/2.3RT. The rate constant for the initial ring opening of radical 1 at 25-degrees-C is 2.9 x 10(10) s-1, which ranks this reaction as one of the fastest radical rearrangements known. The putative product of the initial cleavage reaction, the methylenesecocubyl radical 2, apparently suffers an even faster bond cleavage reaction estimated to be > 1.5 x 10(11) s-1 at 25-degrees-C. The potential utility of methylcubane as a mechanistic probe for oxidation processes that might involve initial hydrogen atom abstraction is noted.