Unimolecular isomerization/decomposition of ortho-benzyne: ab initio MO/statistical theory study

High level molecular-orbital calculations have been carried out to investigate the potential energy surface for the o-benzyne decomposition to 1,3-butadiyne and acetylene as well as that for the isomerization sequence, ortho- to meta- to para-benzyne. The latter species can easily undergo Bergman decyclization. It is shown by statistical theory calculations that the isomerization channel may affect significantly the rate of o-benzyne disappearance in the thermal decomposition process, particularly, at T <2000 K. At 1000 K, the isomerization of o-C₆H₄ to its m- and p-isomers accounts for as much as 99% of the total disappearance rate. The first order rate coefficients for the production of 1,3-butadiyne, meta- and para-benzynes at 100 Torr, 1 atm and 10 atm pressures over the temperature range 1000-3000 K have been calculated for combustion applications.