On the choice of optimal protocol for calculation of 13C and 15N NMR isotropic chemical shifts in nitramine systems

Calculated nuclear magnetic resonance (NMR) chemical shifts (13C and 15N) are reported for the RDX conformers and additional nine cyclic and acyclic nitramines. In order to establish a convenient and consistent protocol to be employed for confirming the experimental 13C and 15N NMR spectra of nitramine compounds, different combinations of models and basis sets were considered. The most reliable results were obtained at B3LYP/6-311+G(2d,p) level and CSGT model and can be used to calculate 13C and 15N NMR chemical shifts with a very high accuracy for nitramine compounds. These results show that the agreement between theoretical and experimental 15N NMR chemical shieldings of nitramines could be used for the evaluation of the intrinsic relationship between structure and explosive properties.