G. Celebre et al., AN INVESTIGATION OF THE CONFORMATION OF 4-CHLOROETHYLBENZENE AS A SOLUTE IN A NEMATIC LIQUID-CRYSTALLINE SOLVENT, Molecular physics, 85(2), 1995, pp. 221-231
The conformation of the ethyl group relative to the phenyl ring plane
in 4-chroroethylbenzene has been investigated by recording and analysi
ng the proton NMR spectrum of a sample dissolved in a nematic liquid c
rystalline solvent. The dipolar couplings obtained are compared with v
alues calculated by the additive potential (AP) and maximum entropy (M
E) molecular mean field theoretical models. In both cases good agreeme
nt between observed and calculated couplings could be obtained only by
adopting a model for rotation about the ring-C bond which allows for
geometry relaxation. The ME method produces a conformational distribut
ion with an absolute maximum at 90 degrees and a secondary maximum at
0, which is also the shape found to give the best fit to the data by t
he AP method. However, constraining the shape of the conformational di
stribution to that found by the molecular orbital calculations and usi
ng the AP method yields an acceptable, if not the best, fit to the dip
olar couplings, and so is the preferred solution. It is concluded that
the inclusion of geometry relaxation on rotation in this molecule is
particularly important when using dipolar couplings to determine the p
otential for rotation about the ring-C bond.