Institute of Chemical Materials, China Academy of Engineering Physics (CAEP), P. O. Box 919-311, Mianyang, Sichuan 621999, China.
Phys Chem Chem Phys. 2019 Jan 30;21(5):2397-2409. doi: 10.1039/c8cp06350h.
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.
长期以来，含能化合物分子内 H 转移被认为是引发分子分解的一个可能的初始步骤。然而，在不同复杂情况下的 H 转移研究还很有限，人们对其在含能化合物中作用的认识还不够全面。在这项工作中，研究了十八个硝基化合物的二十个分子内 H 转移反应，并将其与热力学和动力学中的 NO2 分配进行了比较。确定了三个因素有利于 H 转移，包括分子的高平面性、目标 H 和 O 原子之间的短转移距离以及 H 原子的高质子化。如果 H 转移在动力学上比 NO2 分配更有利，并且如果反向 H 转移的势垒小于 30 kcal/mol，我们将其定义为可逆的。在我们的研究中，对于那些 H50 大于 2,4,6-三硝基甲苯的非撞击感硝基化合物，它们都伴随着可逆 H 转移，而撞击感化合物则没有。因此，我们提出可逆 H 转移可以通过化学能的吸收/释放来有效缓冲外部刺激对分子分解的影响。除了传统的 H 转移引发分子分解的认识之外，这项工作还建立了含能硝基化合物低撞击感与可逆 H 转移之间的新关联。
