A systematic theoretical investigation of the relationship between heats of detonation and NBO charges and 15N NMR chemical shifts of nitro groups in nitramines and nitro paraffins

A new quantitative method for predicting and calculating the heat of detonation for a series of nitro paraffins and nitramines employing the natural bond orbital (NBO) charge analysis and 15N NMR chemical shifts of the nitro group is established. All calculations, including optimizations, charge analysis and 15NNitro NMR chemical shifts, were performed using density functional (DFT) methods with 6-311+G(d,p) basis set. The results show a linear correlation between the nitro group charges and C/N-nitro bond lengths. The latter reflect the strength of the corresponding bond and thus the stability of the nitro compounds. A strong correlation was observed between the heat of detonation with the charge and 15N NMR chemical shift on the nitro group in nitramines and nitro paraffins. Nitro compounds with a higher heat of detonation have less negative nitro group charges, (QNitro) and a lower value for the 15NNitro chemical shift in analogous compounds. From the quantitative models, the heat of detonation increase when the QNitro values (positive coefficient) are larger and decrease when the 15NNitro NMR chemical shift (negative coefficient) is higher. The present work provides consistent models (mean square error prediction values below 0.14 MJ kg−1) in a systematic way for quick estimation of heats of detonation - with or without experimental data - for a wide range of energetic materials. This practical approach is particularly useful as a tool for the design of high-energy density materials.