Wednesday, January 11, 2006

17O NMR from the Warwick group in J. Phys. Chem. A

Cory, please have a look:

Experimental and Theoretical 17O NMR Study of the Influence of Hydrogen-Bonding on C=O and O-H Oxygens in Carboxylic Solids

Alan Wong, Kevin J. Pike, Rob Jenkins, Guy J. Clarkson, Tiit Anupõld, Andrew P. Howes, David H. G. Crout, Ago Samoson, Ray Dupree, and Mark E. Smith*

In Final Form: December 1, 2005

A systematic solid-state 17O NMR study of a series of carboxylic compounds, maleic acid, chloromaleic acid, KH maleate, KH chloromaleate, K2 chloromaleate, and LiH phthalate·MeOH, is reported. Magic-angle spinning (MAS), triple-quantum (3Q) MAS, and double angle rotation (DOR) 17O NMR spectra were recorded at high magnetic fields (14.1 and 18.8 T). 17O 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 17O 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 17O NMR parameters yielded good agreement with the experimental values. Linear correlations are observed between the calculated 17O NMR parameters and the hydrogen bond strengths, suggesting the possibility of estimating H-bonding information from 17O NMR data. The calculations also revealed intermolecular H-bond effects on the 17O NMR shielding tensors. It is found that the S11 and S22 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.

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