Browsing by Author "Frey, H. M."

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Thermal Isomerization of Cyclobutenes: Part 19.—3,3,4,4-Tetrafluorocyclobutcne
(Journal of the Chemical Society : Faraday Transaction - I. The Chemical Society, London. 1972, 68 (10), 1972) Frey, H. M.; Hopkins, R. G.; Vinall, I. C.
The thermal isomerization of 3,3,4,4-tetrafluorocyclobutene has been shown to yield 1,1,4,4- tetrafluorobuta-l,3-diene quantitatively. In the temperature range 306 to 36O'C the reaction is a homogeneous first order essentially irreversible reaction which is almost certainly unimolecular. At pressures above 5.3 kN m~2 (~40 Torr) the rate constant is independent of pressure. High pressure rate constants determined at 10 temperatures in the above range yielded the Arrhenius equation, log kls-1 = 14.09±0.05 —200 600± 500 J mol_1/2.303 RT. At 333.7°C the rate constant was determined over a range of pressures from 0.7 to 9000 N m~2 (0.005 to 70 Torr) and a fall-off curve obtained. The isomerization of this compound is discussed in relation to that of perfluorocyclobutcnc and perfluoro-1,2-dimethylcyclobutene. Ricc-Ramspergcr-Kassel-Marcus calculations have been carried out, and found to fit the fall-off curve quite well. In addition, the effect on the calculated fall-off curve of making extreme changes to the vibrational assignment of the activated complex has been investigated. Finally, various computational procedures have been discussed in relation to the calculation of fall-off curves using deconvolution of the experimental results.
Thermal Unimolecular Decomposition of 1-Ethylcyclohexa-1,4-diene, 1,2-Dimethylcyclohexa-1,4-diene and Bicyclo[4,3,0]nona-l(6),3-diene
(Journal of the Chemical Society : Faraday Transaction - I. The Chemical Society, London. 1972, 68 (7), 1972) Cocks, A. T; Frey, H. M.; Hopkins, R. G.
The pyrolysis of 1-ethylcyclohexa-1,4-diene has been studied from 316 to 379°C in the gas phase at pressures of around 10 Torr. Under these conditions, in an aged reaction vessel, the reaction was strictly first order, and the products, hydrogen and ethylbenzene were formed quantitatively. The rate constants yielded the Arrhenius equation : log k1/s–1= 13.12±0.09–45 870±250 cal mol–1/2.303 RT i.e., log k1/s–1= 13.12±0.09–191 930±1030 J mol–1/2.303 RT The pyrolysis of 1,2-dimethylcyclohexa-1,4-diene in the temperature range 296 to 354°C was found to yield only hydrogen and o-xylene. At pressures between 0.25 and 5.4 Torr which was the range studied, the reaction was strictly first order and the rate constants obtained yielded the Arrhenius equation: log k2/s–1= 12.54±0.03–43 720±80 cal mol–1/2.303 RT i.e., log k2/s–1= 12.54±0.03–182 920±320 J mol–1/2.303 RT. The pyrolysis of bicyclo[4,3,0]nona-1(6), 3-diene yielded hydrogen and bicyclo[4,3,0]nona-1,3,5-triene (1,2-dihydroindene) as the only products. In the temperature range 346 to 408°C and at pressure above 0.8 Torr the decomposition was first order and the rate constants obtained yielded the Arrhenius equation: log k3/s–1= 12.95±0.16–48 580±470 cal mol–1/2.303 RT i.e., log k3/s–1= 12.95±0.16–203 260±1960 J mol–1/2.303 RT. The results obtained in this work are compared with those obtained for the pyrolyses of other cyclohexa-1,4-dienes.