Experimental determination of relationship between intramolecular bond lengths and their stretching vibrational frequencies of N,N-dimethylformamide and acetonitrile molecules in the liquid state

Time-of-flight (TOF) neutron diffraction measurements have been carried out on pure liquid deuterated N,N-dimethylformamide (DMF-d7), acetonitrile (AN-d3), and their concentrated LiTFSA solutions to investigate the effect of intermolecular interaction to intramolecular bond lengths, rCO, of the DMF and rCN of the AN molecules in the liquid state. Intramolecular parameters of DMF and AN are determined by least-squares fitting analyses of neutron total interference terms observed in the high-Q region. Attenuated total reflection (ATR) IR spectra have been measured for pure liquid DMF, AN, and their LiTFSA solutions of natural abundances to determine the average C=O and C equivalent to N stretching vibrational frequencies (nu CO and nu CN) of the DMF and AN molecules, respectively. The relationships between rCO and nu CO for DMF, and between rCN and nu CN for AN, are well approximated by linear functions. The value, d nu CO/drCO = -3,400 +/- 1,600 cm-1 angstrom-1 has been derived for DMF from the slope of the fitted function. d nu CN/drCN = -7,000 +/- 3,000 cm-1 angstrom-1 has been obtained for AN. It has been revealed that the C = O bond length of the DMF and the C equivalent to N one of the AN molecules are sensitively affected by intermolecular interaction. Neutron diffraction and IR measurements have been carried out on pure liquid N,N-dimethylformamide (DMF), acetonitrile (AN), and their concentrated LiTFSA solutions to investigate the relationships between bond length and its stretching frequency in the liquid state. The values, d nu CO/drCO = -(3,400 +/- 1,600) cm-1.angstrom-1 and d nu CN/drCN = -(7,000 +/- 3,000) cm-1.angstrom-1 have been determined for DMF and AN molecules, respectively.