Experimental and theoretical 17O NMR study of the influence of hydrogen-bonding on C=O and O-H oxygens in carboxylic solids

A systematic solid-state O-17 NMR study of a series of carboxylic compounds, maleic acid, chloromaleic acid, KH maleate, K-H chloromaleate, K-2, chloromaleate, and LiH phthalate-MeOH, is reported. Magic-angle spinning (MAS), triple-quantum (3Q) MAS, and double angle rotation (DOR) O-17 NMR spectra were recorded at high magnetic fields (14.1. and 18.8 T). O-17 MAS NMR for metal-free carboxylic acids and metal-containing carboxylic salts show featured spectra and demonstrate that this combined, where necessary, with DOR and 3QMAS, can yield site-specific information for samples containing multiple oxygen sites. In addition to O-17 NMR spectroscopy, extensive quantum mechanical calculations were carried out to explore the influence of hydrogen bonding at these oxygen sites. B3LYP/6-311G++(d,p) calculations of 17 0 NMR parameters yielded good agreement with the experimental values. Linear correlations are observed between the calculated O-17 NMR parameters and the hydrogen bond strengths, suggesting the possibility of estimating H-bonding information from O-17 NMR data. The calculations also revealed intermolecular H-bond effects on the O-17 NMR shielding tensors. It is found that the delta(11), and delta(22) components of the chemical shift tensor at O-H and C=O, respectively, are aligned nearly parallel with the strong H-bond and shift away from this direction as the H-bond interaction weakens.