Nuclear Quadrupole Coupling Constants and Hydrogen Bonding. A Molecular Orbital Study of Oxygen-17 and Deuterium Field Gradients in Formaldehyde-Water Hydrogen Bonding

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A model hydrogen-bond system consisting of formaldehyde and water molecules has been studied by “ab initio” molecular orbital (MO) methods, using a “near-double-zeta” basis set. Quadrupole coupling constants have been calculated for the carbonyl oxygen, the water oxygen, and the hydrogen-bonded deuterium site as a function of the hydrogen-bond geometry. Strong hydrogen-bond formation results in a decrease in the 17O nuclear quadrupole coupling constant of about 2.5 MHz with respect to the non-hydrogen-bonded molecules for both the carbonyl and water oxygen sites. The origins of the decrease are discussed, and comparisons are drawn with experimental 17O NQR data. The calculated deuterium quadrupole coupling constant decreases dramatically with decreasing O…O distance in agreement with available experimental data. The possibility of a negative sign for the 2H quadrupole coupling constant in short, symmetric hydrogen bonds is considered. It seems unlikely that the 2H quadrupole coupling constant is negative in sign for any known O-H…O hydrogen bond. © 1981, American Chemical Society. All rights reserved.

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Journal of the American Chemical Society

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