61142-85-6Relevant articles and documents
Stabilities of Substituted Benzyl Radicals: Dissociation Rates of Amino-, Hydroxy-, and Cyanoethylbenzenes
Suryan, M. M.,Stein, S. E.
, p. 7362 - 7365 (2007/10/02)
Rates of thermal unimolecular decomposition of amino-, hydroxy-, and cyanoethylbenzenes have been determined by the very low pressure pyrolysis technique.Assuming equal A factors, these rates, relative to the rate of dissociation of ethylbenzene, yield the following ortho, meta, and para, respectively, substituent effects on benzylic C-C bond strengths (kcal/mol): NH2, -2.7, -0.3, -1.7; OH, -1.7, -0.7, -1.1; and CN, -0.3, 0.4, -1.5.These effects are generally smaller than those for substituted anisoles and follow different trends.Along with the results of ESR studies of Nicholas and Arnold (Can.J.Chem. 1986, 64, 270), the present substituent effects indicate that a 1-G change in the benzylic hyperfine coupling constant corresponds to a 1.8 kcal mol-1 change in bond strength.
Kinetic Study for Reactions of Nitrate Radical (NO3.) with Substituted Toluenes in Acetonitrile Solution
Ito, Osamu,Akhido, Seiji,Iino, Masashi
, p. 2436 - 2440 (2007/10/02)
The absolute rate constants for the reactions of the nitrate radical (NO3.) with substituted toluenes in acetonitrile have been determined by the flash photolysis method.From the plots of the rate constants against the ionization energies, it was revealed that the reaction path for toluene derivatives with low ionization energies is different from that for toluene derivatives with high ionization energies.For toluene, a deuterium isotope effect was observed to be ca. 1.6, suggesting the direct hydrogen atom abstraction reaction; in this group, xylenes and p-chlorotoluene belong.For toluene derivatives with electron-withdrawing substit uents, NO3. may add to the phenyl rings followed by successive reactions.For both groups, linear correlations against ionization energies with negative slopes show that NO3. is highly electrophilic and that strong polar effects exist in the transition states of both reactions.For toluenes with methoxy groups, the electron-transfer reaction from methoxytoluene to NO3. is a main initial path, since the transient absorption band due to the cation radical of methoxytoluene was detected.
Substituent Effects on Benzyl Radical ESR Hyperfine Coupling Constants. The ?α*Scale Based upon Spin Delocalization
Dust, Julian M.,Arnold, Donald R.
, p. 1221 - 1227 (2007/10/02)
The electron spin resonance spectra of 21 para- and meta-substituted benzyl radicals have been analyzed.A substituent constant, ?α*, has been defined from the benzylic α-hydrogen hyperfine coupling constant.The ?α* constant reflects the component of energy that may be attributed to spin delocalization in a substituted benzyl radical in comparison to the unsubstituted radical.For the derivatives studied, para substitution is stabilizing, except when fluorine is the substituent; meta substitution destabilizes the benzyl radical.A series of radical reactions is reexamined with an extended Hammett relation.The relative importance of spin delocalization vs. polar effects is assessed by the ratio of ρ* to ρ.The importance of choosing substituents for which ?a* and ? differ widely for such an assessment is emphasized.
Intramolecular Electron Transfer and Dehalogenation of Anion Radicals. 3. Halobenzonitriles and Cyanobenzyl Halides
Neta, P.,Behar, D.
, p. 103 - 106 (2007/10/02)
One-electron reduction of halobenzonitriles and cyanobenzyl halides produces the anion radicals which then undergo intramolecular electron transfer leading to dehalogenation.Kinetic spectrophotomethric pulse radiolysis allowed the observation of the halobenzonitrile anion radicals and the determination of their dehalogenation rates.The rates varied from 104 to >107 s-1 depending on the halogen and its position relative to cyano group.The production of X- was measured in steady-state radiolysis experiments, and the participation of cyanophenyl radicals as intermediates was also deduced from observation of chain reaction.The anion radicals of cyanobenzyl halides were not observed since they dehalogenate very rapidly.The cyanobenzyl radicals produced by this process were monitored spectrophotometrically.The rates of dehalogenation of the anion radicals studied here are at least 5 orders of magnitude higher than the corresponding values determined previously for analogous nitro derivatives, but the pattern of reactivities is similar in both series of radicals.
