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The Equilibrium between Localized and Delocalized States of Thermochromic Semibullvalenes and Barbaralanes-Direct
1Institut für Organische Chemie der Universität, Am Hubland, D-97074 Würzburg, Germany, Fax: (+49) 931-888-4606.
Abstract:
The UV/Vis spectra of thermochromic semibullvalenes 1 and barbaralanes recorded at various temperatures yield enthalpy differences between the two degenerate classical structures 1 and 1' and the less stable species (1*) that absorb at long wavelengths. The latter species are interpreted in terms of higher, delocalized states that are located just above the flat potential energy barrier between the ground states (ΔH(0) =11 (R=H; in butyronitrile), 1 kJ mol(-1) (R=Ph)).
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