New insight into the anisotropic effects in solution-state NMR spectroscopy

Abstract

Nuclear magnetic resonance (NMR) spectroscopy is an important technique for structure determination. Within it, anisotropic effects of different functional groups and ring systems, depicted as familiar "anisotropy cones", are broadly used to deduce the stereochemistry, for chemical shift assignments and to explain shielding or deshielding of nuclei spatially close, or directly attached to the corresponding functional group, or ring. Progress in computational methods has enabled the quantification of anisotropic effects, an insight into their origin and to the source of (de) shielding of proximal nucleus. Some widely accepted traditional explanations, presented in NMR spectroscopy textbooks, have been questioned. The purpose of this review is to collect and discuss the research, mainly based on theoretical calculations, that provided new insight into the anisotropic effects, their origin and factors responsible for (de) shielding of proximal protons.