Density functional theory (DFT) calculations show that internal electronegative substituents perturb 3JCOCC Karplus curves by phase shifting them with respect to analogous pathways devoid of this substitution. Thus, the J-coupling maximum, which normally is observed near 180o, is shifted by ~15o. These findings suggest that the two types of inter-residue C-O-C-C coupling pathways observed in many oligosaccharides cannot be treated using a generalized 3JCOCC Karplus equation. Quantitative interpretations of trans-glycoside J-couplings to evaluate linkage conformations will need to take this effect into account.