Effects of Hydrogen Bonding in the Calculation of 15N Chemical Shift Tensors: Benzamide

Abstract

In this communication we present new quantum chemical calculations including the hydrogen bond (HB) interactions that explain the experimental measurements of the {sup 15}N chemical shifts principal values in benzamide and provide a basis for the spatial assignment of the experimental principal components. The results presented in this communication highlight the importance of including HB and, in general, intermolecular interactions in the calculation on {sup 15}N chemical shifts tensors. The findings presented here are not limited to benzamide, but are a general feature in the calculation of {sup 15}N chemical shift tensors. The extreme sensitivity observed in the tensor components from HB indicates that the study of {sup 15}N tensor components may be used to complement the determination of the tertiary structures of molecules of biological significance in solid state samples and/or in frozen solutions. It is well-known that the HB is the principal governing factor in the tertiary structure of biomolecules; therefore the extremely high sensitivity of the {sup 15}N tensor components to these interactions makes {sup 15}N tensors premier indicators of biomolecular structure and portends high value for these NMR methods. Finally, due to the high sensitivity and specificity of tensors, this work emphasizes some of the advantagesmore » of measuring tensor components instead of the traditional isotropic values. 15 refs., 1 fig., 1 tab.« less