Quantitative treatment of lanthanide-induced shifts for some carbohydrate systems where chelation is observed

An approximate model (D) for the calculation of lanthanide-induced shifts or some trans-fused benzylidene acetals which chelate to shift reagents is described. Shifts calculated for the model system 4,5-dimethylveratrole using model D were in good agreement with the reported data. With the aid of model D, rotamer conformations of the methoxyl group on C-1 of methyl 4,6-O-benzylidene-3-O-methyl-α-d-mannopyranoside, methyl 3-O-benzyl-4,6-O-benzylidene-α-d-mannopyranoside, and methyl 4,6-O-benzylidene-α-d-mannopyranoside were investigated.