Gas and liquid phase kinetics of the unimolecular isomerization of 1-chloro-4-bromobicyclo[2.2.0]hexane: The radical stabilization energy of an α-bromine atom
✍ Scribed by Edward N. Cain; Richard K. Solly
- Publisher
- John Wiley and Sons
- Year
- 1972
- Tongue
- English
- Weight
- 530 KB
- Volume
- 4
- Category
- Article
- ISSN
- 0538-8066
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✦ Synopsis
The kinetics of the gas phase isomerization of l-chloro-4-bromobicyclo[2.2.O]hexane to 2-chloro-5-bromohexa-1,5diene have been measured in a static system over the temperature range of 135-215"C, with a variation in the total pressure from 0.6 to 400 torr. For these conditions, the rate constants are well represented by the Arrhenius equation: log (klsec-') = (13.2 f 0.2) -(34.5 f 0.4)/8 where e = 2.303RT kcal/mole. Transition state estimates for the biradical mechanism for the isomerization of bicyclo[2.2.O]hexanes are shown to be in good agreement with these Arrhenius parameters. By comparison of the activation energy with that for the isomerization of bicyclo I2.2.01 hexane and 1,4-dichlorobicyclo (2.2 .O] hexane, the radical stabilization energy of an a-bromine atom is shown to be 1.0 f 1.8 kcal/mole. Rates are also reported in the liquid phase at temperatures of 155°C and 175°C with diphenyl ether, nitrobenzene, and dimethylsulfoxide as solvents. The observed rate constants are all faster (by a factor of 1.1-1.7) than those measured in the gas phase and display no correlation between rate and solvent polarity.