Structure of Liquid N , N -Dimethylformamide Studied by Means of X-Ray Diffraction

Abstract

The structure of N,N-dimethylformamide (DMF) was determined at 25 °C by means of X-ray diffraction using a θ-θ type X-ray diffractometer. The least-squares analysis of the reduced intensities results that a DMF molecule has a practically planar skeletal structure in the liquid state. Intramolecular structural parameters within a DMF molecule were determined as follows: C=O; 1.24 Å, N–C(CHO); 1.35 Å, and N–C(CH3); 1.45 Å. The bond lengths are not appreciably different from those found in the gas phase, except for the C=O length, which is slightly longer by 0.04 Å in the liquid state than in the gaseous one. The radial distribution curve of DMF shows that the intermolecular arrangement of DMF molecules is practically fully disordered and no evidence has been found for the cluster formation of DMF molecules in the liquid state. The experimental result for the weak intermolecular interactions between DMF molecules is supported by ab initio MO-SCF calculations.