Evidence is presented for the covalent binding of biologically reduced metabolites of 2,4,6-15N3-trinitrotoluene (TNT) to different soil fractions (humic acids, fulvic acids, and humin) using liquid 15N NMR spectroscopy. A silylation procedure was used to release soil organic matter from humin and whole soil for spectroscopic measurements. TNT-contaminated soil was spiked with 2,4,6-15N3-trinitrotoluene and 14C-ring labeled TNT, before treatment in a soil slurry reactor. During the anaerobic/aerobic incubation the amount of radioactivity detected in the fulvic and humic acid fractions did not change significantly (11−16%), whereas the radioactivity bound to humin increased to 71%. The 15N NMR spectra of the fulvic acid samples were dominated by a large peak that corresponded to aliphatic amines or ammonia. In the early stages of incubation, 15N NMR analysis of the humic acids indicated bound azoxy compounds. The signals arising from nitro and azoxy groups disappeared with further anaerobic treatment. At the end of incubation, the NMR shifts showed that nitrogen was covalently bound to humic acid as substituted amines and amides. The NMR spectra of the silylated humin suggest formation of azoxy compounds and imine linkages. Bound metabolites possessing nitro groups were also detected. Primary amines formed during the anaerobic incubation disappeared during the aerobic treatment. Simultaneously, the amount of amides and tertiary amines increased. Nitro and azoxy groups of bound molecules were still present in humin at the end of the incubation period. Formation of azoxy compounds from partially reduced TNT followed by binding and further reduction appears to be an important mechanism for the immobilization of metabolites of TNT to soil.

The activation parameters [∆G (200 K), ∆H , and ∆S ] for compounds, together with those for related compounds previously reported in the literature, show that conjugating the degenerate Cope rearrangements of barbaralane (1a) and several semibullvalenes (3a, 7a, 8a), and for those of a subsituents (e. g. aryl, CN, CO 2 R) in the 2,6 positions lower the barriers of the degenerate Cope rearrangement, whereas number of their 3,7-and 2,6-disubstituted derivatives, have been determined by variable-temperature carbon-13 NMR substituents that are electron-withdrawing through the inductive effect (e. g. Cl, CF 3 , SO 2 Ar) retard the reaction. spectroscopy at 126 and 151 MHz. the disubstituted compounds studied include the barbaralanes 1c, d, e, h, j, k, Substituents in the 3,7 positons have little effect or are rateretarding. The presence of 1,5-tri-and -tetramethylene and 2e, h, j, and the semibullvalenes 3d, e, h, 4e, h, i, l, m, and 5hϪ8h. Careful attention has been given to the bridges in semibullvalenes accelerates the rearrangements, the effect being larger in the case of the former. measurement of temperatures. The data for these

We report in this paper the syntheses and the results of an investigation of the structure (delocalized homoaromatic or localized Cope system) of 1,5-dimethyl-2,4,6,8-semibullvalenetetracarboxylic dianhydride 1 and the 5-ethyl analog 2. Although many homoaromatic cationic species are known, there is to date no well-accepted example of an electrically neutral homoaromatic molecule. 1 The semibullvalenes have long been recognized as the system most closely approaching neutral homoaromaticity. 1,2 The Cope rearrangements of semibullvalenes (e.g. 1a a 1b) proceed through the homoaromatic transition state (e.g. 1c) often with very low activation barriers. 1,3 A number of attempts to design semibullvalenes having homoaromatic ground states have been considered. 1 One suggestion, by Paquette, is that the bisannelated semibullvalene (3) might be such a system since the "breathing motion" of the Cope process would be inhibited. 4 Semiempirical 5,6 and ab initio 7 quantum mechanical calculations on other bisannelated semibullvalenes support this hypothesis. Müllen et al. subsequently prepared the first example 8 (4) of a bisannelated semibullvalene and demonstrated that its Cope rearrangement is rapid on the NMR time scale even at -160°C. 10 Similarly, our theoretical studies predict the bisanhydride 1 to have a single minimum potential energy surface with a homoaromatic ground state. 6 The known 11 tetraester 5 was viewed as an ideal precursor to bisanhydride 1. Grohmann's route 11 to 5 (Scheme 1A) was modified to give this tetraester more easily and in improved yield (Scheme 1B). The tetraester 5 was converted to the desired anhydride 1 Via the tetraacid 7 (Scheme 1B).1 proved to be remarkably stable; it can be purified by sublimation (200°C at ambient pressure) and only undergoes slight hydrolysis of one of the anhydride moieties upon prolonged exposure to the atmosphere. This is in contrast with other semibullvalenes, which frequently yield cyclooctatetraene upon mild thermolysis 12 and react more or less readily with oxygen. 10,13 The anhydride 1 crystallizes in space group Cc or C2/c, which are crystallographically indistinguishable. In the latter, the molecule uses a crystallographic 2-fold axis, while in the former no symmetry is imposed on the molecule. Data were all taken on the same crystal with Mo KR radiation to 2θ max of 70°at 293, 243, 163, 148, and 123 K. For the three higher temperatures the refinement of coordinates was straightforward in C2/c (Figure 1a) but not in Cc where the ratio of shifts with respect to error remained high, even though the R-factor was somewhat lower in Cc than in C2/c (0.045 and 0.055, respectively). The difference in R-factors is not significant, because the number of parameters in Cc is twice that in C2/c. An analysis of the thermal ellipsoids in C2/c at room temperature ( Figure 1a) did not agree with rigid body motion. The weighted agreement between observed and calculated components of the thermal ellipsoids is 0.22, while for a rigid motion this is expected to be less...