Karplus-type relationships betweeen scalar coupling constants: 3JHH molecular vs. 4hJHH supramolecular coupling constants
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.