We report density functional molecular dynamic simulations to determine the early chemical events of hot (T=3000 K) and dense (rho=1.97 g/cm(3), V/V-0=0.68) nitromethane (CH3NO2). The first step in the decomposition process is an intermolecular proton abstraction mechanism that leads to the formation of CH3NO2H+ and the aci ion H2CNO2-. This event is also confirmed to occur in a fast annealing simulation to a final temperature of 4000 K at rho=2.20 g/cm(3). An intramolecular hydrogen transfer that transforms nitromethane into the aci acid form, CH2NO2H, accompanies this event. To our knowledge, this is the first confirmation of chemical reactivity with bond selectivity for an energetic material near the Chapman-Jouget state of the fully reacted material. We also report the decomposition mechanism followed up to the formation of H2O as the first stable product. We note that similarities in the global features of reactants, intermediates, and products of the reacting fluid seem to indicate a threshold for similar chemistry in the range of high densities and temperatures reported herein. (C) 2004 American Institute of Physics.