Karplus-type relationships between scalar coupling constants: 3 J HH molecular versus 4h J HH supramolecular coupling constants
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The 3 J HH coupling constants in six H–X–Y–H systems (ethane, methylamine, methanol, hydrazine, hydroxylamine and hydrogen peroxide) and 4h J HH coupling constants in four H–...XH...Y–H, namely [H3NHNH3]+ (two arrangements), HOHNH3 and HOHOH2 have been calculated theoretically as a function of the torsion angle φ. For covalent situations, the corresponding Karplus equations have been fitted to calculated 3 J HH=acos2 φ+bcos φ+c. The a, b and c terms have been analyzed as a function of the electronegativities of X and Y. In the case of ammonium/ammonia complexes (proton shared and not), water/ammonia, and water dimer the values are low (maximum 0.5 Hz) but follow closely a Karplus relationship. Supplementary material is available in the online version of this article at http://dx.doi.org/10.1007/s00214-003-0486-7
KeywordsCoupling constants Karplus relationship Hydrogen bonds Density functional theory calculations
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The present article is dedicated to our friend, Jean-Marie Lehn on occasion of the 15th anniversary of his Nobel Prize. Support was provided by the Spanish DGI (project no. BQU2000–0906). Thanks are given to R. H. Contreras and J. E. Peralta (Universidad de Buenos Aires, Argentina) for allowing the calculation of the coupling constants in their facilities. We warmly thank Janet del Bene for the EOM-CCSD calculations reported in Table 1.