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Molecules 2016, 21(11), 1426; doi:10.3390/molecules21111426

Assessment of the Presence and Strength of H-Bonds by Means of Corrected NMR

Department of Chemistry and Biochemistry, Utah State University, Logan, UT 84322-0300, USA
Academic Editor: Derek J. McPhee
Received: 23 September 2016 / Revised: 19 October 2016 / Accepted: 21 October 2016 / Published: 27 October 2016
(This article belongs to the Special Issue Intramolecular Hydrogen Bonding 2017)
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Abstract

The downfield shift of the NMR signal of the bridging proton in a H-bond (HB) is composed of two elements. The formation of the HB causes charge transfer and polarization that lead to a deshielding. A second factor is the mere presence of the proton-accepting group, whose electron density and response to an external magnetic field induce effects at the position of the bridging proton, exclusive of any H-bonding phenomenon. This second positional shielding must be subtracted from the full observed shift in order to assess the deshielding of the proton caused purely by HB formation. This concept is applied to a number of H-bonded systems, both intramolecular and intermolecular. When the positional shielding is removed, the remaining chemical shift is in much better coincidence with other measures of HB strength. View Full-Text
Keywords: β-sheet; CH··O H-bond; C5 dipeptide; aromatic amino acid; anti-electrostatic H-bond β-sheet; CH··O H-bond; C5 dipeptide; aromatic amino acid; anti-electrostatic H-bond
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This is an open access article distributed under the Creative Commons Attribution License which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. (CC BY 4.0).

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Scheiner, S. Assessment of the Presence and Strength of H-Bonds by Means of Corrected NMR. Molecules 2016, 21, 1426.

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