The results of the previous paper are analyzed to yield information about the reactions of the n-propyl and i-propyl radicals. The various combination and disproportionation reactions are considered. The rate of decomposition of the n-propyl radical was determined as a function of temperature and pressure, and limiting high-pressure and low-pressure kinetic parameters were obtained. The high-pressure activation energy is 32.6 kcal mol-I , and this leads to a value of 24.3 kcal mole ' for the dissociation energy of the C-C bond in the n-propyl radical, to 22.2 kcal mol-' for its heat of formation, and to 99.1 kcal mol-' for the primary C-H dissociation energy in propane. Entropy changes are also calculated from the results.For the decomposition of the i-propyl radical E, = 38.7 kcal mol-', and this leads to 37.7 kcal mol-' for the C-H bond dissocation energy in this radical and to 19.3 kcal mol-' for its heat of formation. The secondary C-H dissociation energy in propane is calculated to be 96.2 kcal mol-'. Corresponding entropy changes are calculated.

Absolute values of the rate constants for the reaction of hydrogen atoms with cyclic olefins in the gas phase have been measured in a discharge-flow system under 3.5, 16, and 22 torr Ar at 23OC. The attenuation of hydrogen atom concentration in the reaction tube in the presence of a large excess of olefin was measured with an ESR spectrometer, and the products were analyzed by gas chromatography. Cyclic Cg hydrocarbons were the only significant products obtained when the hydrogen atom concentration was 2.6 X mole/l., the olefin concentration was in the range of 9 to 22 X lo-* mole/l., and the pressure was 16 torr Ar. The values for the rate constants for reaction with cyclohexadiene-1,3,cyclohexadiene-l,4, and cyclohexene are, respectively, (9 i 2) X lo8, (12 + 1) X lo8, and (6 & I ) X lo8 I./mole-sec, and they are not changed significantly by a sixfold change in total pressure. The fraction of the total interaction that proceeds by addition is 8470 in the cyclohexadiene-I ,3 system, but only I8y0 in The cyclohexadiene-l,4 system, and the cyclohexadienyl radical is therefore the dominant radical species in the latter system. The pattern of interaction between the hydrogen atom and the cyclohexadienyl radical was determined, and comprises 65Y0 of disproportionation, and 13y0 and 23% of combination to yield cyclohexadiene-l,3 and cyclohexadiene-1,4, respectively. These results are consistent with the general patterns of reactivity emerging from studies of the reactions between free radicals and olefins in related systems.

No abstract

No abstract