Application of chemically induced dynamic nuclear polarization to a kinetic study of phenyl radical reactions
1974; Elsevier BV; Volume: 3; Issue: 1 Linguagem: Inglês
10.1016/0301-0104(74)80084-4
ISSN1873-4421
AutoresL. F. Kasukhin, M. P. Ponomarchuk, A. L. Buchachenko,
Tópico(s)Electron Spin Resonance Studies
ResumoThe CIDNP enhancement coefficient of a stable product RX formed in a free radical reaction depends on nuclear relaxation in the paramagnetic precursor R' and decreases with an increase of its lifetime, τR. This dependence was used for evaluation of the lifetime of phenyl radicals generated by thermolysis of N-nitrosoacetanilide (NAA). The value τpb in CCl4 solution at 60° was found to be 6.9 × 10−5 sec which corresponds to a rate constant k = 1.4 × 103 8 mole−1 sec−1 for the reaction Ph + CCl4 → PhCl + CCl3 of which the activation energy equals 8.2 kcal mole−1. During the thermolysis of NAA CIDNP arises in a geminate radical pair (PhN2 ON2Ph)S from which it is transferred to aromatic products through PhNN' and the product of its destruction, Ph' radical. Comparison of the experimental CIDNP enhancement coefficient of the protons in PhNN' radical just leaving the radical pair, with those calculated for different lifetimes of the intermediate gives its mean lifetime τPhN2 = 10−7 sec.
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