In 2-phenyl-1.3-dithiane (1) and its p-methyl derivative (2) theequatorialphenyl adopts a conformation coinciding with the symmetry plane of the molecule. For 2-(2′-methylphenyl)-1.3-dithiane (4) acisoidrelation of theaxialhydrogen on C-2 and the aromatic methyl group was established. This conformation can be changed by substitution of position 2 by methyl: in this geminally substituted compound (3), phenyl no longer assumes theequatorialposition, and the plane of the phenyl group isperpendicularto the symmetry plane of the molecule. These deductions depend on the deshielding effect of sulphur and the diamagnetic anisotropy of the aromatic ring in the NMR spectra influencing the chemical shifts of the orthoprotons and of the protons of the dithiane ring respectively. The influence of the conformation on both of these effects is taken into accoun