Stereochemical aspects of proton chemical shifts—IV: The cumulative nature of the geminal proton shift influenced by long chain substituents

Abstract

Abstract-Substituent shift effects on geminal protons are consistent with cumulative a-, b-and y-effects of a long chain substituent, e.g. whereby not only the first, but also the subsequent B-and y-atoms of the sidechain should be taken into consideration.These shift contributions depend on rotational conformation in a way that lends itself to calculation where the necessary data are available. Therefore the shifts of the unsubstituted parent compound, the individual increment-contributions of the b and y groupings and the rotameric distribution must be known. This would enable, conversely, a semi-quantitative prediction of one of these parameters if the others are accessible.