Thermolysis of Other Cyclopropane Derivatives

Besides undergoing reversible, thermal, geometrical isomerization, cyclopropane also undergoes a slower, irreversible structural isomerization. The kinetics of both reactions of trans-C Hj] cyclopropane at 480 °C in the 10 Torr pressure range have been reported, as well as the kinetics of the structural isomerization of cyclopropane between 454 and 538 °C in the pressure range 0.4—137 atm. First-order kinetics for the gas-phase isomerization of 1,1,2-trimethylcyclopropane between 427 and 481°C have been established. The kinetic data and the formation of the complex mixture of products were interpreted in terms of a unimolecular, biradical-intermediate mechanism, in line with precedent. 

The isomerization of pentachlorocyclopropane to 1,1,3,3,3-pentachloro-propene, which is also first-order in the range 440—490 K between 10 and 50 Torr, like those of other chlorocyclopropanes, is believed to oceur with concerted chlorine atom migration and no intervention of biradical intermediates. Pyrolysis of trans-l,l-dichloro-2,3-dimethylcyclopropane gives both isomerization to trans-3,4-dichloropent-2-ene and direct dehydrohalo-genation to trans-3-chloropenta-l,3-diene. The elimination is the major reaction whereas, from the cis-isomer, the rearrangement is the predominant reaction, as reported previously. 

Thermolysis of (363) with loss of nitrogen gives 7-azabicyclo [4,2,0] oct-7-ene which, though not characterized itself gave stable reduction and hydrolysis products. The 8-spiro-substituted bicyclo[5,1,0]octane (364) undergoes thermal trans - cis isomerization and photo-equilibration. The temperature-dependent photostationary state was 48 52 t rans cis at — 50°C, and the activation parameters for the thermal isomerization are Ai/ = 20.5 kcal mol and AS = — 3.7 cal mol K . A direct measurement of the enthalpy change for the isomerization was made calorimetrically = — 9.0 + 

Reineberg, P. Goodman, P. Vaughan and V. Giorgian, Tetrahedron Letters, 

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