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

The O-17 NMR chemical shifts of 14 N-methylpiperidine-N-oxides and five N-m ethyltetradecahydroacridine-N-oxides were measured. The effects of steric f actors, such as gamma -gauche and 1,3-syn-axial interactions of the N+-O- o xygen, on the O-17 chemical shifts are discussed, and evidence for the main contribution of electrostatic interactions, rather than true steric compre ssion, to the so-called 'steric effects' on O-17 chemical shifts of alcohol s, ethers, sulfoxides and amine oxides is presented. For conformationally m obile compounds, the discussion of the chemical shifts is assisted by resul ts from molecular mechanics (MM+) calculations. Copyright (C) 2001 John Wil ey & Sons, Ltd.