title: Covalency of hydrogen bonds in liquid water can be probed by proton nuclear magnetic resonance experiments.
abstract: The concept of covalency is widely used to describe the nature of intermolecular bonds, to explain their spectroscopic features and to rationalize their chemical behaviour. Unfortunately, the degree of covalency of an intermolecular bond cannot be directly measured in an experiment. Here we established a simple quantitative relationship between the calculated covalency of hydrogen bonds in liquid water and the anisotropy of the proton magnetic shielding tensor that can be measured experimentally. This relationship enabled us to quantify the degree of covalency of hydrogen bonds in liquid water using the experimentally measured anisotropy. We estimated that the amount of electron density transferred between molecules is on the order of 10  m while the stabilization energy due to this charge transfer is ∼15 kJ mol(-1). The physical insight into the fundamental nature of hydrogen bonding provided in this work will facilitate new studies of intermolecular bonding in a variety of molecular systems.
authors.affiliation: Department of Chemistry, Dynamics of Condensed Matter, University of Paderborn, Warburger Street 100, D-33098 Paderborn, Germany.
authors.forename: Hossam
authors.initials: H
authors.lastname: Elgabarty
authors.affiliation: Department of Chemistry, University of Zurich, Winterthurerstrasse 190, CH-8057 Zurich, Switzerland.|Department of Chemistry, McGill University, 801 Sherbrooke Str. West, Montreal, Quebec, Canada H3A 0B8.
authors.forename: Rustam Z
authors.initials: RZ
authors.lastname: Khaliullin
authors.affiliation: Department of Chemistry, Dynamics of Condensed Matter, University of Paderborn, Warburger Street 100, D-33098 Paderborn, Germany.|Paderborn Center for Parallel Computing and Institute for Lightweight Design with Hybrid Systems, Warburger Street 100, D-33098 Paderborn, Germany.
authors.forename: Thomas D
authors.initials: TD
authors.lastname: Kühne