Proton chemical shift tensors in hydrogen-bonded dimers of RCOOH and ROH

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Abstract
In an effort to explain empirically observed correlations between certain structural features of hydrogen bonds and corresponding proton chemical shift parameters determined by single crystal multiple pulse NMR, a theoretical investigation is made of 14 O–H⋅⋅⋅O dimers involving substituted carboxylic acids and alcohols. Nuclear magnetic shielding tensors are calculated for the protons in each hydrogen bond system. Certain linear dependences are observed, in agreement with experimental data, that indicate that the chemical shift tensor is a sensitive measure of hydrogen bonding that can yield more information than the isotropic shift alone. The apparent correlation between the O⋅⋅⋅O separation and isotropic chemical shift is seen to result from the strong dependence of the perpendicular shielding component on the former quantity. The lack of a similar correlation for the chemical shift anisotropy is explained in terms of the parallel component of the shielding tensor. An interpretation of such trends in these proton chemical shift tensors is proposed in terms of existing models of hydrogen bonds.