Structure and Reactivity of Methyl Radical — Cyanide Ion Pairs in Crystal I and Crystal II of Acetonitrile

The extent of interaction between methyl radicals and cyanide ions produced in pairs by dissociative electron capture in the two solid phases of acetonitrile has been studied by e.s.r. using CD313CN. Although no interaction is observed when the radical–anion pairs are generated by photobleaching the acetonitrile dimer radical anion in Crystal I, a very weak interaction as evidenced by an isotropic 13C hyperfine splitting of 3.4 G is found for the corresponding species produced from the acetonitrile monomer radical anion in Crystal II. The rate of hydrogen atom abstraction by the methyl radical in Crystal I is at least a factor of 10 greater than in Crystal II at the same temperature over the range 77–113 K. These results show that the weak perturbation of the methyl radical by the cyanide ion does not enhance methyl radical reactivity in hydrogen atom abstraction. Evidence from 13C hyperfine splitting measurements on [Formula: see text] indicates that the configuration of the methyl radical is planar in these radical–anion pairs. It is emphasized that quantum mechanical tunneling provides a satisfactory explanation for the low apparent activation energies, the curved Arrhenius plots, and the abnormally large deuterium isotope effects which characterize hydrogen atom abstraction reactions by methyl radicals in glassy and crystalline solids at low temperatures. Moreover, since the tunneling rate is extremely sensitive to the width of the barrier, methyl radical reactivity is expected to show a very strong dependence on the precise geometry of the reacting partners in the solid state.

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Initiation mechanisms in radical polymerizations : Reaction of cumyloxy radicals with methyl methacrylate and styrene

Australian Journal of Chemistry ◽

10.1071/ch9822013 ◽

1982 ◽

Vol 35 (10) ◽

pp. 2013 ◽

Cited By ~ 36

Author(s):

E Rizzardo ◽

AK Serelis ◽

DH Solomon

Keyword(s):

Double Bond ◽

Hydrogen Atom ◽

Methyl Methacrylate ◽

Rate Constants ◽

Polymer Structure ◽

Hydrogen Atom Abstraction ◽

Methyl Radicals ◽

Methyl Radical ◽

Constant Rate ◽

Radical Generation

Cumyloxy (1-methyl-1-phenylethoxy) radicals have been generated by thermolysis (60�) of dicumyl hyponitrite in methyl methacrylate and styrene. The carbon-centred radicals formed by interaction of cumyloxyl with the respective monomers were trapped as stable adducts of 1,1,3,3-tetramethyl-isoindolin-2-yloxyl. Extensive hydrogen atom abstraction and methyl radical generation as well as double-bond addition were observed in methyl methacrylate. Styrene underwent only double-bond addition by both cumyloxy and methyl radicals. Some possible implications of these results for polymer structure are discussed. A kinetic study of the decomposition of dicumyl hyponitrite in cyclohexane at various temperatures gave k=7.7 × 1014exp(-13600/T) s-1 for the rate constant. Rate constants for the addition of cumyloxyl to methyl methacrylate (k ≈ 2 × 104 dm3 mol-1 s-1) and styrene (k≈2 × 105 dm3 mol-1 s-1) at 60�have been estimated.

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Evidence for hydrogen atom abstraction by methyl radicals in the solid state at 77.deg.K

Journal of the American Chemical Society ◽

10.1021/ja00732a045 ◽

1971 ◽

Vol 93 (3) ◽

pp. 787-788 ◽

Cited By ~ 40

Author(s):

Ffrancon Williams ◽

Estel D. Sprague

Keyword(s):

Solid State ◽

Hydrogen Atom ◽

Hydrogen Atom Abstraction ◽

Methyl Radicals

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The reaction of hydrogen atoms with ethylene

Proceedings of the Royal Society of London Series A - Mathematical and Physical Sciences ◽

10.1098/rspa.1970.0097 ◽

1970 ◽

Vol 316 (1527) ◽

pp. 575-591 ◽

Cited By ~ 35

Keyword(s):

Hydrogen Atom ◽

Rate Constant ◽

Recombination Reaction ◽

Methyl Radicals ◽

Methyl Radical ◽

Hydrogen Atoms ◽

Ethyl Radical ◽

Cracking Reaction ◽

Computer Calculations ◽

First Time

A detailed study has been made of the products from the reaction between hydrogen atoms and ethylene in a discharge-flow system at 290 ± 3 K. Total pressures in the range 8 to 16 Torr (1100 to 2200 Nm -2 ) of argon were used and the hydrogen atom and ethylene flow rates were in the ranges 5 to 10 and 0 to 20 μ mol s -1 , respectively. In agreement with previous work, the main products are methane and ethane ( ~ 95%) together with small amounts of propane and n -butane, measurements of which are reported for the first time. A detailed mechanism leading to formation of all the products is proposed. It is shown that the predominant source of ethane is the recombination of two methyl radicals, the rate of recombination of a hydrogen atom with an ethyl radical being negligible in comparison with the alternative, cracking reaction which produces two methyl radicals. A set of rate constants for the elementary steps in this mechanism has been derived with the aid of computer calculations, which gives an excellent fit with the experimental results. In this set, the values of the rate constant for the addition of a hydrogen atom to ethylene are at the low end of the range of previously measured values but are shown to lead to a more reasonable value for the rate constant of the cracking reaction of a hydrogen atom with an ethyl radical. It is shown that the recombination reaction of a hydrogen atom with a methyl radical, the source of methane, is close to its third-order region.

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