Saturated amine oxides: Part 4 . Steric and electric field effects on the 17 O NMR chemical shifts of saturated six‐membered azaheterocyclic amine oxides

The 17 O NMR chemical shifts of 14 N ‐methylpiperidine‐ N ‐oxides and five N ‐methyltetradecahydroacridine‐ N ‐oxides were measured. The effects of steric factors, such as γ‐ gauche and 1,3‐ syn ‐axial interactions of the N + —O − oxygen, on the 17 O chemical shifts are discussed, and evidence for the main contribution of electrostatic interactions, rather than true steric compression, to the so‐called ‘steric effects’ on 17 O chemical shifts of alcohols, ethers, sulfoxides and amine oxides is presented. For conformationally mobile compounds, the discussion of the chemical shifts is assisted by results from molecular mechanics (MM+) calculations. Copyright © 2001 John Wiley & Sons, Ltd.