Orientation of the methoxyl group in cis- and trans-2-methoxy-4-methyl-1,3-dioxanes and related compounds as inferred by 1H and 13C nmr spectroscopy. The significance of the "exo-anomeric" effect

摘要: Carbon-13 chemical shifts and 13C—1H couplings are reported for some substituted 2-methoxy-1,3-dioxanes related tetrahydropyran derivatives. These data, together with nuclear Overhauser enhancement experiments, provided evidence a favored orientation of the methoxyl group. From an analysis 13C magnitude vicinal coupling between —OCH3 H-2, possible dynamic-equilibrium group is proposed, evaluation significance "generalized exo-anomeric effect" presented.