AN ELECTRON SPIN RESONANCE STUDY OF KINETICS OF RECOMBINATION OF TRI-T-BUTYLCYCLOHEPTATRIENYL RADICALS

Few measurements of recombination rate constants for hydrocarbon free radicals in liquid solution have been reported. The goal of this work is to measuee the rate of recombination of the tri-t-butylcycloheptatrienyl radical using a simple esr technique. This free radical is generated by photochemical cleavage of hexa-t-butylbicycloheptatrienyl in n-pentane. The recombination rate has been measured (–112° ≤ t ≤ +22°) by terminating the illumination and monitoring the second-order decay of the esr signal on a strip-chart recorder. Absolute rate constants are obtained by comparison of the steady-state esr intensity with that of a solution of di-t-butylnitroxide of known concentration. Typical approximate rate constants are 3 × 104M−1 sec−1 at –105° and 3 × 103 M−1 sec−1 at +22° and the Arrhenius activation energy is 1.7 ± 0.3 kcal/mol. The rate of recombination is compared with that of other hydrocarbon free radicals in solution. © 1969, American Chemical Society. All rights reserved.