The Liquid Structure of Various Nitriles and N,N-Dimethylformamide Studied by the X-Ray Diffraction Method Using a CCD Detector

Abstract

Abstract The liquid structure of acetonitrile (AN), propionitrile (PN), acrylonitrile (ACN), and benzonitrile (BN) was investigated by the transmission mode X-ray diffraction method with a newly developed CCD detector at room temperature and one atmospheric pressure. The nitriles were shielded in a thin wall glass tube. The reduced intensities, si(s), extracted from the measured intensities were compared with those obtained by the X-ray diffraction measurements with the θ–θ type reflection mode for benzonitrile and N,N-dimethylformamide (DMF) as the reference. In all the nitriles it was found that molecules are arrayed in the zigzag form as found in previous studies for AN. The non-bonding N···C (nitrile carbon) distance between the anti-parallel adjacent molecules was 340 pm for all nitriles. The intermolecular C···C distance between next neighbour molecules was 420 pm for CH2···CH2 in AN, 430 pm for CH3···CH3 in PN, 425 pm for CH···CH in ACN, and 390 pm for C6H5···C6H5 in BN. The short C6H5···C6H5 distance was explained in terms of the π–π stacking interactions of the aromatic rings. DMF molecules interact each other through dipole–dipole interactions, and the O···C distance of 320 pm at the O···H–CO– interaction through the formyl proton may partly contribute to the intermolecular interactions. The distance between parallel DMF molecules in a plane was estimated to be 743 pm. The diffraction data were well explained in terms of a weak layered structure of DMF, and the layers were separated by about 365 pm.