Comparison of GIAO and CSGT for calculating ¹³C and ¹⁵N nuclear magnetic resonance chemical shifts of substituent neutral 5-aminotetrazole and 5-nitrotetrazole compounds

The comparison of the gauge-including atomic orbital (GIAO) and the continuous set of gauge transformation methods for calculating nuclear magnetic chemical shifts (CSs) mainly at density functional levels of theory are presented. Isotropic ¹³C and ¹⁵N magnetic CS for 14 compounds of tetrazoles are reported. Compared with establishing a convenient and consistent protocol to be employed for confirming the experimental ¹³C and ¹⁵N NMR spectra of tetrazole compounds, different combinations of functionals and basis sets were considered. The most reliable results were obtained at GIAO/B3LYP/aug-cc-pVDZ with integral equation formulation for the polarizable continuum model (PCM), which has the smallest root mean square errors and can be used to calculate ¹³C and ¹⁵N NMR CS with a very high accuracy for tetrazoles. These results show that the accurately calculated ¹⁵N NMR CS of tetrazoles could be used for the evaluation of the intrinsic relationship between structure and explosive properties.