Wide-line 1H NMR study of 4′-(pentyloxy)-4-biphenylcarbonitrile in different phase states

Abstract

A sample of 4′-(pentyloxy)-4-biphenylcarbonitrile was studied in the temperature range 20–70°C by wide-line 1H NMR. The line shapes, half-widths, and second moments were determined. At 20°C, the spectrum is a broad structureless line, which was split into three components at temperatures above 47°C. This pattern persisted up to 65°C, with the components becoming narrower. Above 68°C, the spectrum rapidly collapses to give a structureless narrow line with a width δH < 0.01 G. Analysis of the spectra and comparison with theoretical calculations made it possible to elucidate the transition of the sample from the crystalline to the nematic and isotropic phases, as well as to determine the temperature range of the stability of the liquid-crystalline phase and the role of rotational mobility of protons of different functional groups and sometimes of these groups as a whole in the mechanisms of phase transitions.