Disproportionation–combination reactions of cyclohexyl radicals at low temperature in the solid state

Abstract

The disproportionation–combination ratio of cyclohexyl radicals has been measured at low temperatures (135–195 K) in a variety of solid phases, cyclohexane, cyclo-octane, benzene, camphane and water. The radicals were generated by carrying out the reaction C₆H₁₁Br + Na·→C₆H₁₁·+ NaBr, using the rotating cryostat technique. When allowance is made for the occurrence of side and secondary reactions the values of the ratio k_d/k_c were found to lie in the range 0.44 to 1.1 depending on the temperature and solid used. These values are close to those found in liquid cyclohexane (1.1) and in the gas phase (0.5) at ambient temperatures. The fact that the ratio is only slightly influenced by marked changes in reaction conditions suggests that though the transition states must be different, these differences are very small as far as the energies and the volumes of the states are concerned.