Influence of N–H…O and O–H…O hydrogen bonds on the 17O, 15N and 13C chemical shielding tensors in crystalline acetaminophen: A density functional theory study

Abstract

A computational investigation was carried out to characterize the 17O, 15N and 13C chemical shielding tensors in crystalline acetaminophen. We found that N–H…O and O–H…O hydrogen bonds around the acetaminophen molecule in the crystal lattice have different influences on the calculated 17O, 15N and 13C chemical shielding eigenvalues and their orientations in the molecular frame of axes. The calculations were performed with the B3LYP method and 6–311++G(d, p) and 6–311+G(d) standard basis sets using the Gaussian 98 suite of programs. Calculated chemical shielding tensors were used to evaluate the 17O, 15N, and 13C NMR chemical shift tensors in crystalline acetaminophen, which are in reasonable agreement with available experimental data. The difference between the calculated NMR parameters of the monomer and molecular clusters shows how much hydrogen-bonding interactions affect the chemical shielding tensors of each nucleus. The computed 17O chemical shielding tensor on O(1), which is involved in two intermolecular hydrogen bonds, shows remarkable sensitivity toward the choice of the cluster model, whereas the 17O chemical shielding tensor on O(2) involved in one N–H…O hydrogen bond, shows smaller improvement toward the hydrogen-bonding interactions. Also, a reasonably good agreement between the experimentally obtained solid-state 15N and 13C NMR chemical shifts and B3LYP/6–311++G(d, p) calculations is achievable only in molecular cluster model where a complete hydrogen-bonding network is considered. Moreover, at the B3LYP/6–311++G(d, p) level of theory, the calculated 17O, 15N and 13C chemical shielding tensor orientations are able to reproduce the experimental values to a reasonably good degree of accuracy.