15N CHEMICAL SHIFT CALCULATIONS AND NATURAL BONDING ORBITAL ANALYSES OF (BENZAMIDE)n = 1 - 6 CLUSTERS.

A DFT/B3LYP study was performed to calculate 15N chemical shielding tensors in (benzamide)n = 1-6 clusters. We found that N–H⋯O hydrogen bonds around the benzamide molecule in crystalline lattice have significant influences on the 15N chemical shielding tensors. For (benzamide)n clusters, the n-dependent trend in 15N chemical shielding appears to be correlated with cooperative effects in R[N–H⋯O] bond distance. Natural bonding orbital (NBO) analysis was used to rationalize the chemical shielding results in terms of $n \to \sigma_{{\rm N-H}}^\ast$ charge delocalization effects in the benzamide clusters. This suggests that 15N chemical shielding measurements can provide a useful probe of electron delocalization phenomena in both gaseous and condensed media. [ABSTRACT FROM AUTHOR]