The conformational analysis of saturated heterocycles. Part XXXIII. 1-t-Butylpiperidine-4-spiro-4′- and -5′-(2′,2′-dimethyloxazolidine) and a discussion of steric compression effects on chemical shifts

Abstract

The title compounds, and a 3′-methyl analogue of the former, have been prepared and their low-temperature n.m.r. spectra studied to elucidate their conformational equilibria and hence allow deductions regarding the steric requirements of the formally sp³-hybridised NH and NMe groups and the oxygen atom in comparison with a methylene group. Evidence for deshielding by steric compression is reviewed, and it is shown that this can cause protons attached to axial groups to resonate at lower field than the equatorial analogues