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 3 J (aa), 3 J (ae) and 3 J (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 [ 3 J (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 Δ J (aa) and Δ J (ae) [Δ J = J (exp)‐ J (calc)] along each carbon‐carbon bond in the pyranose systems reveals an unexpected degree of geometrical homogeneity.