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 axialâ equatorial free-energy differences for N-methyl groups in this series are measured.