The Equilibrium between Localized and Delocalized States of Thermochromic Semibullvalenes and Barbaralanes-Direct Observation of Transition States of Degenerate Cope Rearrangements

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...

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Bibliographic Details
Published in:Angewandte Chemie International Edition 1999-04, Vol.38 (8), p.1064-1067
Main Authors: Quast, Helmut, Seefelder, Maximilian
Format: Article
Language:English
Subjects:
Barriers
Cope rearrangements
Enthalpy
Flats
Ground state
Homoaromaticity
Potential energy
Spectra
Transition states
UV/Vis spectroscopy
Valence isomerization
Wavelengths
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Summary: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 (ΔH0=11 (R=H; in butyronitrile), 1 kJ mol−1 (R=Ph)).
ISSN:1433-7851
1521-3773
DOI:10.1002/(SICI)1521-3773(19990419)38:8<1064::AID-ANIE1064>3.0.CO;2-U