Gas-phase hydroxyl radical reactions. Products and pathways for the reaction of hydroxyl with aromatic hydrocarbons

Abstract

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...

Formation of ring‐retaining products from the OH radical‐initiated reactions of benzene and toluene

“…The formation of the cresol isomers has been reported previously [8,9,11,12,15,16,19,20,23,27], although, as in this work, m-+ p-cresol Nitrotoluenes have been identified as products of the OH radical reaction with toluene under simulated atmospheric conditions in several previous studies [9,12,15,21,23,27] (in some of these studies, only m-nitrotoluene was reported [ 15,231). Hoshino et al [9] observed m-and p-nitrotoluene, but no o-nitrotoluene, with the p-nitrotoluene yield generally being less than that of the m-nitrotoluene isomer.…”

Rate constants for the gas-phase reaction of hexamethylbenzene with OH radicals and H atoms and of 1,3,5-trimethylbenzene with H atoms

“…The observation that mesitol is the main product under these experimental conditions is in line with the result of an earlier flow-tube study [11]. The 70 eV EI spectrum of mesitol shows the strongest peaks at m/z ϭ 77 (10), 91 (25), 121 (100), 135 (32), and 136 (79) amu not affecting the signals of the aromatics at m/z ϭ 105 and 120 amu for TMB and m/z ϭ 147 and 162 amu for HMB.…”

Gas‐phase reaction of hydroxyl radicals with m‐, o‐ and p‐cresol

“…Phenol, the cresols, and the dimethylphenols are formed in significant yields (2–60%) from the gas‐phase reactions of OH radical with benzene, toluene, and the xylenes, respectively 1,21–33. In contrast with results from previous studies [1,21–28,30–32, Bohn and Zetzsch 34, Klotz et al 29, Knispel et al 35, and Volkamer et al 33,36 have observed a pronounced dependency between the NO x concentrations and the distribution of the aromatic degradation products. The phenol yields formed from the benzene reaction with OH were found essentially constant for NO x levels of up to several 10 ppb and decrease for elevated NO x concentrations (>100 ppb) 33.…”