Abstract
It has been found that the behavior of hydrogen atoms produced by the homolitic scission of the C-H bond is quite different at 4.2 and 77/sup 0/K. Neopentane--isobutene (2 mol percent) mixtures irradiated at 77/sup 0/K show that tert-butyl radicals are formed by hydrogen atom scavenging in addition to neopentyl radicals. The scavengeable hydrogen atoms are estimated to be about 60 to 70 percent of the hydrogen atoms produced in the system. However, the same mixture irradiated at 4.2/sup 0/K gives only neopentyl radicals which amount to the same as the total radical yield in the mixture irradiated at 77/sup 0/K. This indicates that the hydrogen atoms which are scavengeable at 77/sup 0/K are not scavenged at 4.2/sup 0/K and they reacted with neopentane forming neopentyl radicals. The ESR line width of the neopentyl radicals, their pairwise trapping, and microwave power saturation behavior indicate that the hydrogen atoms reacted with neopentane by a rather short-range reaction at 4.2/sup 0/K while some of them reacted with solutes via long-range migration at 77/sup 0/K. Similar effects of irradiation temperature have been also found in neopentane--cyclohexane (2 mol percent) mixtures as well as in neopentane containing a small amount of impurity. It ismore » suggested that short-range hot abstraction from neopentane takes place at 4.2/sup 0/K while a long-range tunneling reaction of thermal hydrogen atoms with solutes takes place at 77/sup 0/K other than hot abstraction. The results are discussed in relation to guest radical formation in mixed crystals of n-decane-d/sub 22/ and n-decane-h/sub 22/ previously reported.« less
Published Version
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