A maximum - entropy analysis of the problem of the rotameric distribution for substituted biphenyls studied by ' H nuclear magnetic resonance spectroscopy in nematic liquid crystals

The statistical principle of maximum entropy is applied to the analysis of dipolar couplings from 'H NMR of nonrigid molecules dissolved in liquid-crystalline phases. A distribution function for the orientational and inter-ring angles is so obtained. The most probable internal angle q7 is determined for 4,4'-dichlorobiphenyl (q? = 340) in the nematic phase of 152, 4pentyl-4'-cyanobiphenyl (q? = 32°) and 4'-Br-4-Cl-2,6-difluorobiphenyl (q = 42°) in EBBA. The physical reliability of the distributions determined is discussed. The maximum-entropy treatment seems to indicate a limit for the information on the internal motion obtainable from the experimental data.