Saturated amine oxides: Part 8 †. Hydroacridines: Part 27 ‡. Effects of N ‐oxidation and of N ‐quaternization on the 15 N NMR chemical shifts of N ‐methylpiperidine‐derived mono‐, bi‐, and tricycloaliphatic tertiary amines

The 15 N chemical shifts of 13 N ‐methylpiperidine‐derived mono‐, bi‐ and tricycloaliphatic tertiary amines, their methiodides and their N ‐epimeric pairs of N ‐oxides were measured, and the contributions of specific structural parameters to the chemical shifts were determined by multilinear regression analysis. Within the examined compounds, the effects of N ‐oxidation upon the 15 N chemical shifts of the amines vary from +56 ppm to +90 ppm (deshielding), of which approx. +67.7 ppm is due to the inductive effect of the incoming N + O − oxygen atom, whereas the rest is due to the additive shift effects of the various C ‐alkyl substituents of the piperidine ring. The effects of quaternization vary from −3.1 ppm to +29.3 ppm, of which approx. +8.9 ppm is due to the inductive effect of the incoming N + CH 3 methyl group, and the rest is due to the additive shift effects of the various C ‐alkyl substituents of the piperidine ring. The shift effects of the C ‐alkyl substituents in the amines, the N ‐oxides and the methiodides are discussed. Copyright © 2007 John Wiley & Sons, Ltd.