Molecular Order versus Conformation Changes in the Liquid-Crystal Phases

Deuteron magnetic resonance splittings and their temperature dependence from deuterated liquid-crystal compounds are analyzed in terms of molecular conformation and orientational order. Three order parameters are found to be necessary to explain the smectic-$C$ (${\mathrm{S}}_C$) spectra whereas only two are required for the nematic (N), ${\mathrm{S}}_A$ and ${\mathrm{S}}_B$ phases. The data are consistent with the concept that the preferred conformation of the molecule remains unchanged at the N-${\mathrm{S}}_C$, N-${\mathrm{S}}_A$, and ${\mathrm{S}}_A-{\mathrm{S}}_B$ phase transitions as well as throughout the temperature range of these phases.