A theoretical investigation of hydrogen bonding effects on oxygen and hydrogen chemical shielding tensors of aspirin

A computational investigation was carried out to characterize the O-17 and H-1 chemical shielding ( CS) tensors in crystalline aspirin. It was found that O-H center dot center dot center dot O and C-H center dot center dot center dot O hydrogen bonds around the aspirin molecule in the crystal lattice have a different influence on the calculated O-17 and H-1 CS eigenvalues and their orientations in the molecular frame of axes. The calculations were performed with the BLYP, B3LYP, and M06 functionals employing 6-311++G(d,p) standard basis set. Calculated CS tensors were used to evaluate the O-17 and H-1 chemical shift isotropy (delta(iso)) and anisotropy (Delta sigma) in crystalline aspirin, 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 CS tensors of each nucleus.