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-alpha),N-alpha (with alpha = 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 Moller-Plesset (MP2) perturbation level of theory. PMR spectra predict a large downshift of delta(H) = 7.9 ppm in heptaazacubane owing to the more number of nitrogen and the stronger C-(HN)-N-. . . interactions. These chemical shifts are explained by the net atomic charges derived from the population analysis based on Hirshfeld partitioning scheme. (c) 2006 Elsevier B.V. All rights reserved.