STUDIES OF CAGE REACTIONS .2. COMBINATION OF CH3 RADICALS AND OF CH3 AND CF3 INTO CF3CH3

Cage combination of methyl radicals formed by photolysis of CH3N=NCH3 was investigated in eight solvents at four different temperatures. The probability of combination p(CH3) = C2H2/N2 was accounted for by Noyes' treatment; i.e., 1/p(CH3) is a linear function of T1/2/* for each solvent, although slightly different lines were obtained for different solvents. The results led to the conclusion that the probability of combination, α, on each collision is three to five times as high for CH3 radicals as for CF3 radicals. This may be accounted for by the higher rate of rotation of CH3 when compared with CF3. As in the previous study, logP(CH3) = log{(C2H6/N2)/[1-(C2H6/N2)]} vs. 1/T is found to be linear, and the lines obtained for all the solvents are again parallel to each other. This constancy of Ec - Ed (the difference of formal “activation energies”) is striking. Its value is -1.6 ± 0.2 kcal/mole for CH3 cage combination, whereas for the reaction of CF3 radicals Ec - Ed = - 2.6 ±0.1 kcal/mole. The mixed cage combination of CH3 and CF3 into CH3CF3 shows similar features; p(CH3,CF3) and P(CH3,CF3) are between those found for the homocombinations of CH3 and of CF3 and the respective Ec - Ed = -2.1 kcal/mole. © 1968, American Chemical Society. All rights reserved.