CONFORMATIONAL DEPENDENCE OF THE ONE-BOND CARBON PROTON COUPLING-CONSTANTS IN OLIGOSACCHARIDES

A study is presented of the dependence on conformation of one‐bond carbon‐proton coupling constants in three 1‐4‐linked disaccharides. Calculated 1J(CH) values are based on the FPT formulation in the semi‐empirical INDO MO method. The configuration at the anomeric carbon influences the 1J(CH) value, and the 1J(C‐1′, H‐1′) values are 20–30 Hz higher than the 1J(C‐4, H‐4) values. The conformational dependence of 1J(CH) on the dihedral angle about the CO bonds is satisfactorily expressed in the analytical form 1J(CH) = A cos 2ϕ + B cos ϕ. The constants A‐E are different for the α‐ and β‐anomers. Calculated average values 〈1J(C‐1′, H‐1′)〉 = 163.7 Hz and 〈1J(C‐4, H‐4)〉 = 146 Hz for methyl β‐xylobioside using PCILO‐calculated abundances of conformers agree well with the experimental values of 162.7 and 147.5 Hz, respectively. Copyright © 1990 John Wiley & Sons, Ltd.