The influence of the stereochemistry of the nitrogen centre on proton chemical shifts and on 1H–1H and 15N–1H spin–spin coupling in tetrahydro-1,3-oxazines

Abstract

The nuclear magnetic resonance spectra of a series of tetrahydro-1,3-oxazines are described. The spectral parameters are discussed in terms of the stereochemistry at the nitrogen centre. The C-2 chemical shift differences are influenced by the orientation of both the lone pair and the N-substituent, whereas only the orientation of the lone pair seems to affect the C-2 geminal coupling constant. The axial–equatorial free-energy differences for N-methyl groups in this series are measured.