Influence of Stacking Interactions on NMR Chemical Shielding Tensors in Benzene and Formamide Homodimers as Studied by HF, DFT and MP2 Calculations

A systematic investigation of the dependencies of the isotropic chemical shielding and the chemical shielding anisotropy upon the vertical-stacking distance for the respective 15 N, 1 H, and 13 C nuclei present in simple models representing the aromatic and nonaromatic stacking (i.e., in benzene and formamide dimers accordingly) has been carried out. Although the approaches employed differ in the way they treat the effects of electron correlation and hence their ability to account for the energetics of stacking varies significantly, the qualitative characteristics of the stacking-induced variation in the chemical shielding parameters remain unchanged. This substantiates the use of the computationally cheap, DFT-based methods (the SOS-DFPT-IGLO strategy in particular) in modeling the secondary structural effects on chemical shielding parameters of biomolecular systems.