Predicting heats of explosion of nitrate esters through their NBO charges and 15N NMR chemical shifts on the nitro groups

Employing natural bond orbital (NBO) charge analysis and 15N NMR chemical shifts of nitro groups (15NNitro) as independent variables, a good theoretical quantitative model was built to predict the heats of explosion for 20 nitrate esters. All calculations, including optimizations, charge analysis and 15NNitro NMR chemical shifts, were performed using density functional (DFT) methods with a 6-311+G(d,p) basis set. The results show a positive linear correlation between the nitro group charges and the O-Nitro bond lengths. Strong correlations were also observed between the heats of explosion and the charges (R2 = 0.9704) and the 15N NMR chemical shifts (R2 = 0.9719) of the studied compounds. Nitrate esters with higher heats of explosion had more positively charged nitro groups (QNitro) and had lower values for the 15NNitro chemical shifts of the analogous compounds. These tendencies are similar to those observed for the nitramines and nitro paraffins. The root mean squared error of prediction (RMSEP) for the experiment, in regards to the predicted heats of explosion for the fourteen nitrate esters and based on the quantitative model, is below 0.22 MJ kg−1. Based on these results, this practical approach could be a useful tool in the design of high energetic materials based on nitrate esters.