engleski

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 CuKα beam produces a molecular structure of the title compound that was in disagreement with IR, 1H and 13C NMR data. Vibrations of the double C=C 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 Csp2–Csp2 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 Csp2–Csp2 bond disguising the correct molecular structure. Density functional theory, M06-2X with 6-311G(d, p), was used to distinguish static from dynamic disorder.

structure evaluation ; refinement of incorrect model ; disorder ; low-temperature data ; high-quality data

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