The thermal stabilities of a number of nitroarenes were examined in solution and in condensed phase. In general, increasing the number of nitro groups decreased thermal stability. Changing the substituent on 1-X-2,4,6-trinitrobenzene from X = H to NH2 to CH3 to OH accelerated decomposition; this effect was attributed to increased ease of intramolecular proton transfer to an ortho nitro group, thus weakening the carbon-nitrogen bond. In solution, the effect of increasing substitution from n = 1 to n = 3 on X(n)(NO2)(3)C6H3-n was uniformly that of decreasing the thermal stability of the species. However, in condensed phase, results suggested that crystal habit may be more important than molecular structure; for X = Br, CH3, and NH2, the more substituted species was the more stable.