Microscopic evidence that the nitromethane aci ion is a rate controlling species in the detonation of liquid nitromethane.

We present microscopic evidence that the aci ion (H2CNO-2) of nitromethane (H3CNO2) plays an important role in the detonation kinetics of liquid-phase nitromethane. It is known from previous detonation experiments that very minute additions of organic bases (e.g., amines) have a profound effect on the detonation properties of nitromethane; i.e., the explosive is strongly sensitized. Here we show that, under conditions similar to the detonation experiments, the only new chemical species generated in nitromethane by the bases sodium hydroxide (NaOH), diethylenetriamine (NH2CH2CH2NHCH2CH2NH2), and pyridine (C5H5N) is the aci ion, within the sensitivity of the experiments. The primary tool used to demonstrate this is 13C NMR spectroscopy. Ab initio quantum-mechanical calculations of the chemical shifts are used to support the experimental interpretation. Qualitative arguments concerning the increased reactivity of the aci ion, relative to normal nitromethane, are given. We review earlier work and relate it to the current findings. [ABSTRACT FROM AUTHOR]