Theoretical studies on NMR chemical shifts in azacubanes

Successive substitution of CH groups of cubane (CH)8, by isoelectronic nitrogen atoms leads to a class of energy-rich azacubanes (CH)8-αNα (with α = 1–8). In the present work, we systematically investigate how substitution of nitrogen in a cubanoid influence deshielding of carbon and manifest in the chemical shift in NMR spectra calculated using the second order Møller-Plesset (MP2) perturbation level of theory. PMR spectra predict a large downshift of δH = 7.9 ppm in heptaazacubane owing to the more number of nitrogen and the stronger C–H⋯N interactions. These chemical shifts are explained by the net atomic charges derived from the population analysis based on Hirshfeld partitioning scheme.