Aromatic contributions, methyl groups

Table 7 also indicates that the rate enhancements for a 3- and 5-methyl group vary significantly among 1,2-azoles. The difference between the increments in log units for a 3-and 5-methyl group, which should vary directly with bond fixation in the ground state, is larger for isoxazole (1.4) than for pyrazole (0.7) and for isothiazole (0.2). This indicates that the aromaticity increases in the same order and contributes the first quantitative evidence that the 1,2-azoles follow the same aromaticity order as furan < pyrrole < thiophene. 

In the production of TNT from the reaction between toluene and mixed acids (nitric/sulfuric), TeNMe forms in amounts between 0.2—0.4% of the total wt of TNT. This TeNMe has been held responsible for several expins which have occurred in TNT plants, causing fatal injuries to personnel and severe damage to facilities. These expins were attributed to the presence of TeNMe in the acid fume lines and the acid storage tanks. Mixts of TeNMe and readily oxidizable materials are known to form very powerful and sensitive expl mixts. Since TeNMe is also isolated from the nitration of Nitrobenzene (NB), the TeNMe formed in the nitration of toluene may arise from the oxidation of the aromatic ring and/or methyl group. In an effort to gain more informa-. tion on the origin of TeNMe from TNT production, radioactive carbon-14 (14C) was used as a tracer to determine the extent to which each of the carbon atoms in the toluene skeleton of the various nitro-substituted isomers contributes to... 

The largest single contribution (54.2%) is from ring carbon-1 attached to the methyl group, and the bulk (94%) of the TeNMe formed is via oxidation of the aromatic ring... 

The aromatic rings contribute to the polycarbonate s high glass transition temperature and stiffness (Table 4.4). The aliphatic groups temper this tendency giving polycarbonate a decent solubility. The two methyl groups also contribute to the stiffness because they take up... 

Theoretical calculations support the expectation that the preferred site of initial OH attack is ortho to the methyl group (Andino et al., 1996), but addition to the other positions also occurs. If the OH-aromatic adduct, which contains 18 kcal mol-1 excess energy, is not stabilized, it decomposes back to reactants, reaction ( — 62). The existence of the adduct in the case of the OH-benzene reaction has been observed spectroscopically (Fritz et al., 1985 Knispel et al., 1990 Markert and Pagsberg, 1993 Bjergbakke et al., 1996). As expected for such a mechanism, the rate constants at temperatures below 300 K exhibit a pressure dependence at lower pressures. At higher temperatures, the rate of decomposition of the excited adduct back to reactants is higher, so the net contribution of adduct formation to the overall reaction is small compared to H-abstraction. 

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