The N.M.R. spectra of symmetrical meta disubstituted benzenes in a nematic phase at room temperature

Abstract

The N.M.R. spectra of meta dichloro and meta dibromo benzenes are analysed in the nematic phase of 4-methoxy benzylidene-4-amino-α-methyl cinnamic acid-n-propyl ester at room temperature. The direct couplings are found to be of negative sign. The molecules orient preferentially with the aromatic plane along the direction of the magnetic field and the C ₂-symmetry axis perpendicular to it. The relations between the various direct couplings and the inter-proton distances are reported. The ratio of the distance between the meta protons along the axis perpendicular to the C ₂ symmetry and the ortho protons is determined precisely. The other ratios could not be determined to any reasonable precision. The reasons are discussed. The angles between the C-H bonds of the equivalent protons and the C-C bonds in both the molecules are determined on the assumption of the C-H bond lengths and the ring geometry of benzene.