Thermal Behaviour of C 8 H 8 Hydrocarbons Gas‐Phase Thermolysis of Cuneane, a New Example of a High‐Strain Energy Release Process

The kinetics of thermal decomposition of cuneane 2) ( 1 ) in the gas phase have been investigated in the temperature range 180–220°C. The reaction is a clean first‐order homogeneous process leading to the formation of two C 8 H 8 isomers, viz., semibullvalene 3) ( 2 ) and cyclooctatetraene ( 3 ). The rate constant varies with temperature according to the Arrhenius equation log( k/S −1 ) = (13.82 ± 0.09) – (37.7 ± 0.2 kcal mol −1 )/ RT In10. The Arrhenius parameters are consistent with a biradical mechanism leading to the formation of semibullvalene ( 2 ). The product proportions are pressure‐dependent which strongly suggests that semibullvalene ( 2 ) is initially formed with high vibrational energy content (ca. 74 kcal mol −1 ) and can react further to give cyclooctatetraene ( 3 ).