Prediction of anti and gauche vicinal proton-proton coupling constants in carbohydrates: A simple additivity rule for pyranose rings

The effect of the relative orientation and electronegativity of substituents on the magnitude of ³J(aa), ³J(ae) and ³J(ee) is well predicated by a simple set of additivity constants, valid for pyranose rings in carbohydrates. The proposed set of parameters is used to calculate 327 coupling constants ³J(HH)] in a variety of pyranosides and related compounds. A comparison with experimental values taken from the literature shows that couplings in molecules which are conformationally pure and underformed can be predicted with a surprising accuracy. An overall root-mean-square agreement of 0.29 Hz is attained for a selected group of 305 coupling values. A statistical breakdown of ΔJ(aa) and ΔJ(ae) ΔJ=J(exp)-J(calc)] along each carbon-carbon bond in the pyranose systems reveals an unexpected degree of geometrical homogeneity.