Thermal isomerisation of methyl-, trifluoromethyl-, methoxy-, and hydrogen-substituted fluorinated benzene isomers

Abstract

Fluorinated benzene isomers C₆F₅X, where X = H, Me, CF₃, and OMe, have been found to isomerise cleanly to the benzene form by a homogeneous first-order process. The logarithms of the rate constants (sec.^–1) for these isomerisations in the gas phase between 40 and 170 °C are: C₆F₅H: (A) 12·5 – 25,500/2·3RT, (B) 12·4 –25,600/2·3RT; C₆F₅Me : (A) 14·2 – 30,600/2·3RT, (B) 14·4 – 29,800/2·3RT; C₆F₅CF₃: (A) 13·8 – 28,200/2·3RT, (B) 13·4 – 29,600/2·3RT; C₆F₅OMe: (B) 11·7 – 25,900/2·3RT. Here (A) is thought, though identifications are not inarguable, to be the Dewar isomer with the group substituted on the tertiary carbon atom and (B) the isomer with the group substituted on the double bond.