Proton Magnetic Resonance Spectra of Benzene and Benzene-1-13C in Isotropic and in Nematic Solution

Abstract

Th ¹H-NMR-spectra of benzene and benzene-1-¹³C in the isotropic phase (CCl₄ solution) as well as in the nematic phase of a liquid crystal are analysed and the resulting direct and indirect couplings presented. The comparison of observed direct couplings with values calculated from known Raman structural data shows deviations of up to 9% relative to the HH_(orto) -coupling. This corresponds to an apparent increase of the carbon-proton distance of 0.03 A. Possible reasons are discussed such as anisotropy of the indirect couplings, solvent effects on indirect couplings and intramolecular vibrations. The conclusion is reached that the consideration of intramolecular vibrational motion perfectly explains the discrepancies.