Thermal Isomerisation of Substituted Semibullvalenes and Cyclooctatetraenes – A Kinetic Study

Autor: Thomas Dietz, Helmut Quast, Markus Heubes, Alexander Witzel, Wolfgang R. Roth, Martin Boenke
Rok vydání: 1999
Předmět:
Zdroj: European Journal of Organic Chemistry. 1999:813-822
ISSN: 1099-0690
1434-193X
Popis: Whereas 1,5-dimethylsemibullvalene (1b) equilibrates with 1,5-dimethylcyclooctatetraene (2b), the semibullvalene-2,6-dicarbonitriles 13 rearrange irreversibly to afford mixtures of the isomeric cyclooctatetraene-1,5-dicarbonitriles 14 and 15. Arrhenius and Eyring parameters of these thermal isomerisation reactions have been determined for the gas phase (1b 2b) and [D6]benzene solutions (1b 2b, 13 14 + 15). Furthermore, the activation parameters of the known rearrangement of octamethylcyclooctatetraene (3) to octamethylsemibullvalene (4) have been determined. – The data for these compounds, together with those for related compounds previously reported in the literature, show that substituents not only influence the relative stabilities of the semibullvalene and cyclooctatetraene systems but also the height of the energy barrier for their interconversion. Those substituents that lower the barrier toward the degenerate Cope rearrangement of semibullvalenes simultaneously accelerate their rearrangement to cyclooctatetraenes thus limiting the thermal stability of the former.
Databáze: OpenAIRE
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