The adventure playground of mechanisms and novel reactions. (Reihe: Profiles, Pathways, and Dreams, Reihenherausgeber: J. I. Seeman. ) Von R. Huisgen. American Chemical Society, Washington, 1994, 279 S., geb. 24.95 $. – ISBN 0‐8412‐1832‐3

Thermal Rearrangements of Perchlorohexatrienes-Structures and Experimental and Theoretical Evaluation of Pathways to Isomerization and Cyclization

We have prepared trans- (1) and cis-octachloro-1,3,5-hexatriene (2) by known routes and studied their thermal behavior experimentally and theoretically by ab initio calculations. The three double bonds in 1 and 2 are completely decoupled due to steric hindrance by the eight Cls, as indicated by calculations as well as the single-crystal X-ray structure of 1. The cis isomer 2 can be isomerized to the trans isomer 1 by heating it to 220–250 °C either neat or dissolved in high-boiling solvents, leading to a roughly 2:1 mixture of trans and cis isomers. Calculations at several different levels of theory predict 1 and 2 to be isoenergetic within 2 kJ mol–1. Unimolecular cis/trans isomerization i…