Structure and Intramolecular Motions in Triethylenediamine as Studied by Gas Electron Diffraction

The structure and intramolecular motions in triethylenediamine have been investigated by gas electron diffraction with a parallel study of bicyclo[2.2.2]octane in our previous paper. The structural parameters determined by a least-squares analysis on molecular intensities, with estimated limits of error, are as follows: rg(C–N)=1.472±0.007 Å, rg(C–C)=1.562±0.009 Å, ∠C–C–N=110.2±0.4°, ∠C–N–C=108.7±0.4°, rg(C–H)=1.110±0.012 Å and ∠H–C–H=111.5±5.6°. The gas-phase structure is in good correspondence with that in the crystal phase determined by Weiss et al. by X-ray diffraction. The potential function with regard to the twisting motion around the C3 symmetry axis is shown to have a broad minimum around the D3h conformation, being quite analogous to that for bicyclo[2.2.2]octane; in terms of the torsional angle φ about the C–C axis, it probably has a small hump of the order of 100 cal/mol at φ=0° and a double minimum around φ=10°. The above study was made with a new nozzle assembly, by which the sample can be heated to about 200°C. The detail of the design and operation is described.