The Kinetics of alkyl radical reactions with aliphatic alcohol glasses as studied by electron spin resonance

Abstract

Methyl radical reactions with matrix molecules in glasses C2H50H, (CH20H)z, n-and i-C3H70H, n-and i-C4HsOH, n-and i-CSHIlOH, C~DSOH, and i-C:+D70D, and the reactions of C:2H5, C3H7, C4H9, C :~H I~ with methanol glasses have been studied. Alkyl radicals were produced by photolysis of diphenylamine-alkylhalide-alcohol mixtures using ultraviolet light.In all cases the alkyl radical decay follows the law c = c g exp(-h 4). The 4 law should not be associated with alkyl radical diffusion in a matrix. A method of processing the kinetics of those reactions in which one paramagnetic species changes into another with the total concentration being constant and the electron spin resonance spectra of both species overlapping, is described.

The √t law in solid‐phase reactions verification of the √t law stability in h‐atom abstraction reactions

“…The results are shown in Figure 2. The mean value of K = 0.4 min-'I2 coincides with that obtained for the matrix immediately after freezing [4]. The mean K value for methyl radical reaction in annealed methanol (Fig.…”

“…The mean K value for methyl radical reaction in annealed methanol (Fig. 3) equals 0.65 min-1/2, whereas earlier we adduced 0.72 min-lI2 for methanol immediately after freezing [4]. However, this difference does not exceed that obtained Reaction kinetics for methyl radicals in ethanol a t 77 K. (l), after anduring half a year in similar experiments over a period of one-half year with samples immediately after freezing.…”

“…When prepared and frozen to 77 K, the samples were annealed a t the reaction temperature during a certain time interval and then subjected to ultraviolet light. Figures 1-3 depict the kinetic data obtained as described in [4]. It is seen that after aging, in all cases the radicals decay by the same law.…”

“…The absolute value of the total free radical concentration was about (1-2) X 1017 ~m -~. The technique did not differ from that described in [4], except for ethyl radicals which were obtained from CzHsI. When prepared and frozen to 77 K, the samples were annealed a t the reaction temperature during a certain time interval and then subjected to ultraviolet light.…”

Intermolecular hydrogen tunneling in solids. Comparison between diabatic and adiabatic rate expressions

“…A typical example would be hydrogen exchange between a methane molecule and a trapped methyl radical in solid methane. Theoretically more complicated but experimentally more accessible is the equivalent reaction of methyl and methanol (1)(2)(3)(4)(5)(6)(7)(8)(9)(10)(11)(12)(13)(14). In both cases hydrogen transfer is opposed by a high potentialenergy barrier which reduces the rate of transfer over its top to negligible values at the low temperatures where these materials are solid.…”