DiscussionW. H. Duewer (Lawrence Livermore Laboratory). The stationary state assumption for various free radicals has been tested by other modelers and found to be satisfactory for several. The large discrepancies found by the authors suggest errors either in the formulation of the model or of the steady state expression. Because only a few terms were included in the steady state approximations used, I suspect the latter. If there is no error (e.g., omitted significant terms) then the significant differences between your model and other models that cause your model not to behave 2483 as a steady state species should be described. In the case of

Photooxidation of cumene (isopropylbenzene) and pyridine in dilute solution in natural waters gives products characteristic of reactions with alkylperoxy (RO(2).) and hydroxyl (HO.) radicals. On the basis of the rates of formation of the products, the average concentrations of RO(2). and HO. are estimated to be about 10(-9) and 10(-17) mole per liter, respectively. The concentration of RO(2). is large enough that, for some classes of reactive chemicals, oxidation can be an important process in natural waters.

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Y) Y (Z) Flgure 1. Axis system in C=O and N-0 bonds: X = C, N.atoms, as compared with the values for otherwise similar but non-hydrogen-bonded atoms.7 The experimental data presented here corroborate the theoretical results (see also Figure 2 of ref 7 ) .In addition to the direct study of hydrogen bonding in the form of geometrical interpretation of the I7O NQR data, the results presented here and in the previous paper facilitate the analysis of the electronic effects that are reflected in the I7O NQR data. For example, the carbonyl group in 4(1H)-pyridinone is structurally similar to that in p-benzoquinone, but has a quite different quadrupole coupling constant, 8.33 vs. 11.51 MHz.14 A large portion of the difference in the values of the quadrupole coupling constant is probably due to the effect of hydrogen bonding in 4(1H)-pyridinone, although the solid-state structure of this compound is not known. If we assume that the length of the hydrogen bond is the same as is found in 2(1H)-pyridinone (2.77 A),'5 then we can estimate the effect of hydrogen bonding on the 170 quadrupole coupling constant to be about 1.0 MHz. Because this still leaves a large difference of 2.2 MHz between the two oxygen sites, one can infer that there exists a significant difference in the electronic environment of the two carbonyl groups. The lower quadrupole coupling constant in 4( 1H)-pyridinone suggests a much larger oxygen 2p, population.In summary, we have presented 1 7 0 NQR data for several hydrogen-bonded systems. The experimental data support the results of a previous theoretical study. The results demonstrate that hydrogen bonding in the solid state is amenable to study by 170 NQR techniques. Secondly, the effects of hydrogen bonding upon the electric field gradient can be estimated, thus aiding in the further analysis of intramolecular electronic effects on the 1 7 0 NQR data. ~ ~~~~~ (14) Hsieh,Y.; Koo, J. C.; Hahn, E. L.The reactions of OH with benzene, toluene, 1,4-dimethylbenzene, and 1,3,5-trimethylbenzene have been investigated in a discharge flow system at total pressures of 6-12 torr. In the presence of NO, NOz, and O2 the intermediate radicals are converted quantitatively to stable products from which two major reaction pathways are identified. Abstraction of a hydrogen atom from the methyl group by OH leads primarily to the corresponding aldehyde, and addition to the aromatic ring by OH gives primarily the corresponding phenols. Nitro substitution of the aromatics via the OH adduct competes with phenol formation; however, the amount depends on the ratio of NOz/Oz. In the case for toluene, the ratio of rate constants, kNOf/kol, for the two processes is (4 f 2) X lo3. The isomer distributions for OH addition to toluene were determined to be 0.806 f 0.022 ortho, 0.051 f 0,009 meta, 0.143 & 0.019 para, and <0.008 ipso. The contributions of methyl attack (k,) relative to total reaction (kl + k2) are 0.15 f 0.02 for toluene, 0.15 f 0.02 for 1,4-dirnethylbenzene, and 0.021 f 0.006 for 1,3,5-trimethylbenzene. IntroductionArom...

This review covers hydrogen-atom transfer from carbon-hydrogen bonds in organic compounds to chlorine atom, methyl, ethyl, trichloromethyl, t-butoxy and alkylperoxy radicals in the liquid phase. Rate constant data are presented-iri 38 tables. Literature is covered throu,gh most of 1972. The review is divided into six sections; an introduction plus five sections each dealing with specific radicals. Hydrogen-atoIn trander to chlorine Iltom Ilrp pre!':f>ntp{l :I!': rpbtivp ratp eon",tant",_ For hydrogen-atom transfer to methyl, ethyl, trichloromethyl, and t-butoxy radicals, both relative and absolute rate constants are tabulated. For alkylperoxy radicals only absolute rate constants are listed. Each absolute rate constant ha.s a tabulated set of rate parameters where A has been assigned and E derived from the Arrhenius equation.

The autoxidation of 1,4-cyclohexadiene proceeds exclusively through a free radical chain dehydrogenation to form benzene and hydrogen peroxide. The key step is the reaction of the cyclohexadienyl radical with oxygen to give benzene and hydroperoxy (HO2•) radicals directly. Estimated Arrhenius parameters exclude other routes. The bond energy of the active carbon-hydrogen bonds in various carbon radicals correlates directly with the amount of olefin formed in competition with organic hydroperoxide upon reaction with oxygen.The formation of benzene and hydrogen peroxide from the oxidation of 1,4-cyclohexadiene1'2 is one of the few cases of dehydrogenation by a simple autoxidation process at room temperature. While this oxidation is atypical because of the thermodynamic advantage associated with benzene formation, other hydrocarbons show the same behavior at higher temperatures. Because of the potential of this reaction as a source of hydroperoxy radicals near room temperature, we have made a careful study of the reaction.

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