Conformational disorder of dioxane ring in a crystal of 2,5-di(isopropylamide)-3,4-ethylenedioxythiophene

The X-ray structure analysis based on high-quality single-crystal data obtained at room temperature and 100 K using a high-intensity Cu Kα beam produces a molecular structure of the title compound that was in disagreement with IR, 1H and 13C NMR data. Vibrations of the double CC bond lack in IR spectrum whereas signals of two methylene groups are visible in the 1H NMR spectrum. 13C NMR shows a spectrum of a C2 or Cs-symmetric compound with a corresponding signal at 65.05 ppm characteristic for saturated carbon atoms in dioxane rings. The two chemically different models can be derived from the results of refinement: (a) model comprising two conformers of dioxane ring, and (b) presence of dioxene ring in which a conformational disorder simulates a Csp2Csp2 bond. Both models were refined and compared with spectroscopic data that definitely ruled out a presence of dioxene ring. Conformational disorder of dioxane ring in a crystal of 2,5-di(isopropylamide)-3,4-ethylenedioxythiophene simulates Csp2Csp2 bond disguising the correct molecular structure. Density functional theory, M06-2X/6-311G(d, p), was used to distinguish static from dynamic disorder.