SATURATED AMINE OXIDES: Part 7. HYDROACRIDINES: Part 26. EFFECTS OF N-OXIDATION ON THE ~(13)C NMR CHEMICAL SHIFTS OF SATURATED SIX-MEMBERED AZAHETEROCYCLIC TERTIARY AMINES. PREDICTION OF THE CHEMICAL SHIFTS OF THE AMINE OXIDES

摘要

The ~(13)C NMR chemical shifts of 38 saturated monocyclic, bicyclic and tricyclic piperidine-derived amine oxides are compared with those of their parent amines, and the stereostructural parameters accounting for the shift differences are identified and determined quantitatively by multilinear regression analyses. The results indicate that nitrogen electron lone-pairs in saturated tertiary amines exert γ-gauche effects of roughly the same magnitude as a N-methyl group, and γ-anti effects sizeable larger than a N-methyl group or a N~+—O~- oxygen atom. The obtained shift increments allow quite accurate chemical shift predictions for the amine oxide carbons located in the β-, γ-, and δ-positions with respect to the N~+—O~- oxygen, provided the molecular geometry (certain dihedral angles) of the amine oxide and of its parent amine is fairly well known.