2315proton transfer, desorption of the neutrals, recombination in the vapor phase. The C-N bond must cleave for this to happen with PTTN. Some of the nitrogen oxides that appear could result from oxidation-reduction reactions associated with the C-N bond fission.(3). Within 1 s of the initial product formation, the hydrocarbon residue is attacked, probably by HN03 and the nitrogen oxides, resulting in the formation of H 2 0 , C02, CO, HNCO, and HCN by what is, no doubt, a complex series of reactions. The fact that HCN(g) becomes increasingly prevalent while NH4N03(g) becomes unimportant when external gas pressure is applied suggests that C-N bond rupture leading to N H 3 evolution is strongly suppressed by pressure.In summary, the decomposition of PTTN begins at the extremities of the cation with N-H bond fission. It progresses inward, first cleaving the C-N bonds and finally involves the C-C bonds. This pattern is consistent with degradation of the cation by reaction with an external agent. H N 0 3 appears to be that agent (23) Inami, S. H.; Rosser, W. A.; Wise, H.
Supplementary Material Available:Tables SI-SI11 containing listings of observed and calculated structure factors, the anisotropic temperature factors, hydrogen atom coordinates (9 pages). Ordering information is given on any current masthead page.Single crystals of nitromethane in diamond-anvil cells at pressures of 0.3 to 6.0 GPa have been studied by X-rays at room temperature. The crystal structure is similar to the low-temperature, ambient-pressure structure. Below 3.5 GPa hydrogen atoms could not be located. At 3.5 GPa the methyl group is rotated about 4 5 O from the position in the low-temperature form. Raman data taken at pressures up to 11.7 GPa showed all molecular vibrational frequencies to increase with pressure.
IntroductionThe pressureinduced chemistry of small molecules has recently been shown to be a fruitful area of investigation. In particular, studies of the decomposition of N O a t moderate pressures have shown a facile transformation to N 2 0 , NO2, and N203.1 An especially interesting result in the N O system is that two different structural modifications of NzO4 exist but only one of the forms exhibits a further pressure-induced reaction to nitrosonium nitrate, N O N 0 3 . This result suggests the importance of topochemical pathways for pressure-induced chemical changes.Nitromethane is one of the simplest organic explosive compounds. As such, it is a good candidate for study under temperature and pressure extremes. Brasch, has reported that at 150 O C and 5.0 GPa nitromethane undergoes an irreversible decomposition to C02 and a solid material that is probably ammonium oxalate. More recently3 the formation of methazonate ion has been observed in the thermal base-catalyzed decomposition of nitromethane at ambient pressure.In an attempt to learn more about the chemical and physical properties of nitromethane, we have made single-crystal X-ray studies in a diamond-anvil cell at nine pressures from 0.3 to 6.0 GPa at room temperature. I...
