Kinetic and equilibrium study of gas‐phase interconversions of 1,3,6‐cyclooctatriene, 1,3,5‐cyclooctatriene and bicyclo[4.2.0]octa‐2,4‐diene

The gas‐phase equilibrium and rate constants for the isomerizations of 1,3,6‐cyclooctatriene (136COT) to 1,3,5‐cyclooctatriene (135COT) [reaction (1)] and bicyclo[4.2.0]octa‐2,4‐diene (BCO) to 135COT [reaction (‐2)] have been measured between 390 and 490 K and between 330 and 475 K, respectively. The rate constant of reaction (1) obeys the Arrhenius equation\documentclass{article}\pagestyle{empty}\begin{document}$$k_{\rm 1} = 10^{10.93 \pm 0.08} {\rm exp}[- (115.9 \pm 0.7{\rm kJ}/{\rm mol})/RT]{\rm s}^{ - 1}$$\end{document}The corresponding equilibrium constant is given by the van′t Hoff equation\documentclass{article}\pagestyle{empty}\begin{document}$${\rm In K}_{\rm 1}^{\rm 0} = (0.24 \pm 0.04) + (13.78 \pm 0.15{\rm kJ}/{\rm mol})/RT$$\end{document}The strain energy of the 136COT ring is calculated to be 31.7 kJ/mol, based on the known value of 37.2 kJ/mol for 135COT, and Δ H   f 0 (298 K) for gaseous 136COT is 196.3 kJ/mol. The rate constant of reaction (‐2) obeys the Arrhenius equation\documentclass{article}\pagestyle{empty}\begin{document}$$k_{{\rm - 2}} = 10^{12.38 \pm 0.23} {\rm exp}[(- 106.9 \pm 1.5{\rm kJ}/{\rm mol})/RT]{\rm s}^{ - 1}$$\end{document}The equilibrium constant for 135COT ⇆ BCO fits the van′t Hoff equation\documentclass{article}\pagestyle{empty}\begin{document}$${\rm In K}_{\rm 2}^{\rm 0} = (- 1.20 \pm 0.02) - (0.40 \pm 0.07{\rm kJ}/{\rm mol})/RT$$\end{document}The strain energy of the BCO skeleton is calculated to be 108.3 kJ/mol, and Δ H   f 0 (298 K) for gaseous BCO is 183.3 kJ/mol.