PMR studies on N-methyl formamide oriented in a liquid crystalline nematic phase

Abstract

The PMR spectrum of N-methyl formamide dissolved in the nematic phase of 4-methoxybenzylidene-4-amino-α-methyl cinnamic acid-n-propyl ester is reported. The four interproton dipolar coup- lings are derived. Using reasonable values for the bond lengths and the bond angles, it is found that the results are consistent with the molecule having a plane of symmetry containing the fragment H.CO.NH.C. Assuming the H-CO-N fragment to be rigidly planar, this plane of symmetry may ' effectively' arise also from two rapidly interconverting conformations in which the remaining two bonds meeting at the nitrogen atom are bent either below or above this plane; the angles of bend are less than 10°. Information on the mode of rotation of the methyl group about the N-C bond is derived. The results establish that N-methyl formamide contains predominantly the ' trans ' species NH and the C=O groups in the trans position ). In addition, some weak lines, which arise from the ' cis ' species ( NH and the C=O group in the cis position ) present to a much smaller extent are detected.