Deuterium quadrupolar parameters and geometry of nitrobenzene from 1H and 2H NMR spectra using liquid crystal solvents

Abstract

The 1H NMR spectra and 13C satellites of nitrobenzene and nitrobenzene- 15N in PCH and ZLI nematic phases, respectively, were recorded and analyzed. The dipolar couplings obtained, corrected for the harmonic vibration, yielded two detailed r α structures, coinciding within the experimental error limits ( r CH ortho = 1.087 A ̊ , r CH meta = 1.062 A ̊ , r CH para = 1.089 A ̊ ). The 1H and 2H NMR spectra were then recorded on two solutions containing both nitrobenzene and nitrobenzene- 2H 5 in the PCH and ZLI nematic phases, respectively. The two sets of order parameters for nitrobenzene obtained from the 1H spectra were assumed to describe also the orientation of nitrobenzene- 2H 5 in the two solutions. The three pairs of quadrupolar splittings for the three deuterated positions yielded by the deuterium spectra were used, together with the r α structure and with the order parameters, to determine the quadrupolar coupling constants and the asymmetry parameters of the three deuterons ( 2 H ortho: DQCC = 209 ± 2 kHz, η = −0.06 ± 0.01; 2 H meta: DQCC = 183 ± 3 kHz, η = 0.06 ± 0.02; 2 H para: DQCC = 179 ± 4 kHz, η = 0.08 ± 0.04 ). The results for the ortho deuteron deviate strongly from the usual values for aromatic CD bonds. Some possible explanations are suggested.