Reversible intramolecular hydrogen transfer: a completely new mechanism for low impact sensitivity of energetic materials

Abstract

The intramolecular H transfer of energetic NO₂-compounds has been recognized as a possible primary step in triggering molecular decomposition for a long time. Nevertheless, studies on H transfer in different complex situations are limited, lacking a comprehensive understanding of its role in NO₂-compounds. In this work, twenty intramolecular H transfer reactions are studied for eighteen nitro compounds and compared with the NO₂ partition in thermodynamics and kinetics. Three factors, including the high planarity of molecules, the short transfer distance between the target H and O atoms and the high protonation of the H atom are identified to facilitate H transfer. If H transfer is more kinetically favorable than NO₂ partition, and if a reverse H transfer occurs with a barrier less than 30 kcal mol⁻¹, we define it as a reversible one. In our study, for those impact insensitive nitro compounds with H₅₀ larger than that of 2,4,6-trinitrotoluene, all of them are found to be accompanied with reversible H transfer, while the impact sensitive compounds are not. Accordingly, we propose that the reversible H transfer can effectively buffer the external stimuli against the molecular decomposition through chemical energy absorption/release. Beyond the conventional understanding that H transfer triggers molecular decomposition, this work builds a new correlation between reversible H transfer and the low impact sensitivity of energetic nitro-compounds.