Karplus-type relationships between scalar coupling constants: 3JHH molecular versus 4hJHH supramolecular coupling constants
The 3JHH coupling constants in six H–X–Y–H systems (ethane, methylamine, methanol, hydrazine, hydroxylamine and hydrogen peroxide) and 4hJHH 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 3JHH=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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