Proton, Deuteron, and Nitrogen Resonance of Dimethylformamide in Nematic Polypeptide Liquid Crystals

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Abstract
An experimental study of proton, deuteron, and nitrogen resonance of dimethylformamide and deuterated DMF has been made in oriented nematic liquid crystals of poly‐L‐glutamic acid. The solvents used were various mixtures of DMF and H2O or D2O. From the proton spectra the complete order matrices were determined for each solvent system. From consistency between the solvent systems the angle HCN of the amide could be determined and was found to be 107± 1° . From the observed quadrupole splittings of all deuterium nuclei and of nitrogen in (deuterated) DMF in three solvent systems, all elements of the quadrupole coupling tensors of these nuclei were obtained. The quadrupole coupling constants and asymmetry factors found were: for the amide deuteron 197 kHz, 0.13; for the methyl deuterons trans to the amide oxygen 46 kHz, 0.19 and for those cis to the amide oxygen 64 kHz, 0.06 (averaged over methyl rotation); for the nitrogen 3.3 MHz, 0.4. Deuteron quadrupole splitting of solvent water was also observed, while proton dipole splitting of water did not occur because of too fast proton exchange.