VIBRATIONAL-SPECTRA AND MOLECULAR-CONFORMATIONS OF 1,4-DIIODOBUTANE, 1,5-DIIODOPENTANE AND 1,6-DIIODOHEXANE

The infrared and Raman spectra of 1,4-diiodobutane, 1,5-diiodopentane and 1,6-diiodohexane have been taken for samples in both the liquid and the solid state. A systematic normal coordinate calculation has been carried out in order to analyse the observed spectra and determine the conformations of these molecules. 1,4-Diiodobutane crystallizes in the gauche-trans-gauche' conformation in the stable solid and in the trans-trans-trans conformation in the metastable solid. The rotational isomerism of this molecule previously proposed was therefore revised accordingly. 1,5-Diiodopentane and 1,6-diiodohexane were found to assume the all-trans conformation in the crystalline solid state. It is shown that many conformers coexist in the liquid state of these molecules. © 1979.