Molecular orbital calculations of the proton-proton coupling constants in nucleosides

Molecular orbital calculations of proton-proton coupling constants are carried out for a number of nucleosides as a function of conformational characteristics of these compounds. The study of the role of the ring puckering and of the orientation of the exocyclic CH₂OH group on the vicinal coupling constants of the ribose indicates the existence, in solution, of an equilibrium between several conformations. The influence of the torsion angle around the glycosidic bond on the vicinal and long range coupling constants is also examined.