Structure and Rotational Isomerism of Ethylenediamine as Studied by Gas Electron Diffraction

The structure and the rotational isomerism of ethylenediamine have been investigated by means of gas electron diffraction. Evidence has been given for the presence of one conformer (gauche) in the vapor phase (at 50–120°C); the N–C–C–N dihedral angle measured from the cis position is 64·0±4°, and the fraction of any other isomer, if present, is estimated to be less than 5%. A theoretical prediction based on the SCF-CNDO/2 method has essentially accounted for this finding. The rg distances and the angles based on the ra structure determined by a least-squares analysis on molecular intensities, with estimated limits of error, are as follows: C–C=1.545±0.008 Å, C–N=1.469±0.004 Å, ∠C–C–N=110.2±0.7°, C–H=1.109±0.01 Å, ∠C–C–H=111·9±5°, and ∠H–C–H=112·7±8°.