What Parameters Determine N−N and O−O Coupling Constants (2h J X - X) Across X−H+−X Hydrogen Bonds?

• Published in: The journal of physical chemistry. A, Molecules, spectroscopy, kinetics, environment, & general theory Molecules, spectroscopy, kinetics, environment, & general theory, 2001-02, Vol.105 (5), p.930-934
• Main Authors: Del Bene, Janet E, Perera, S. Ajith, Bartlett, Rodney J
• Format: Article
• Language: English
• ISSN: 1089-5639; 1520-5215
• DOI: 10.1021/jp003470o

Equation of motion coupled-cluster calculations (EOM-CCSD) have been performed to obtain 15N−15N and 17O−17O coupling constants (2h J X - X) across N−H+−N and O−H+−O hydrogen bonds in a series of protonated dimers. 2h J X - X values are dominated by the Fermi-contact term and are distance dependent. Large coupling constants are associated with symmetric hydrogen bonds, short hydrogen bond distances, and low electron densities on the hydrogen-bonded proton, and are not related to the binding energies of these complexes. The magnitudes of coupling constants do not appear to be related to the nature of the covalent bonding of the hydrogen-bonded nitrogen and oxygen atoms, although this bonding indirectly determines the coupling constant by determining the N−N or O−O distance. Complexes with sp2-hybridized oxygens are more sensitive to the trans or cis orientation of the hydrogen-bonded pairs than are the corresponding nitrogen complexes. One-bond coupling constants (1h J X - H) are greater than two-bond couplings (2h J X - X) in complexes with symmetric hydrogen-bonds, but 1 J N - H is greater than 2h J N - N which is greater than 1h J N - H for nonsymmetric hydrogen bonds. When reduced coupling constants are used for comparison, 2h K X - X is always greater than 1 K X - H, which is greater than 1h K X - H.