The rotating sector technique has been used to determine the rate of recombination of trifluoromethyl radicals produced by the vapor phase photolysis of hexafluoroacetone. Using the method of calculation described in Part I of this paper the rate constant was found to be 2.3×1013 cc mole—1 sec—1 at 127°C.
The photolytic decomposition of hexafiuoroacetone has been used to produce trifluoromethyl radicals for a study of their reactions with hydrogen isotopes. Activation energies for the four reactions : CF3 + HZ + CF3H, CF3 + HD + CF3H, CF3 + HD 3 CF3D and CF3 + D2 3 CF3D were found to be, respectively, 9-5 f 0.7, 10.5 f 15, 102 f 1.5 and 10-2 4 0.7 kcal mole-1. The results are discussed in detail in terms of the collision theory and the absolute theory of reaction rates. Evidence is adduced for a progressive decline in pre-exponential factor down the series of reactions: H + H2, CH3 + H2, CF3 + H 2 .
A study of the electron spin resonance spectra of radicals trapped in y-irradiated polycrystalline alkyl halides at -196°C has established that in almost all cases the main species observed in the first hours after irradiation is the parent alkyl radical, though isomerization reactions such as isobutyl+ tert-butyl occur at this temperature.Hyperfine splitting constants for the interaction of the a-and &protons with the unpaired electron have been determined for radicals with the formulae (CH~),~H~_,(IZ = 0 to 3)RCHzdHz, RR'CHeHz, RR'dH (including cycloalkyl) and RR/R"d. It is found that a-protons and those in freely rotating methyl groups interact to give isotropic hyperfine splitting of 60-75Mc/secY while the magnitude of the interaction of the &protons may vary from <12 to >130Mc/sec, depending on the configuration of the radical. In particular, the two fi-protons in RCH2CH2 are not equivalent, implying an unsymmetrical equilibrium configuration. The relevance of these conclusions to the identscation of trapped radicals is discussed.
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