Abstract:Equilibrium and kinetic studies on the title reaction show that the two isomers (1) and (2) are interconverted by a reversible unimolecular reaction, and lead to values for the enthalpy and entropy differences of the two isomers and activation parameters for their interconversion.
“…When perfluorohexaethyl benzene ( 87 ) vapor is subjected to low-pressure pyrolysis at 400 °C, it is transformed into its Dewar isomer 86 . This very remarkable reaction occurs because it is 50 kcal/mol less endothermic than the formation of 84 from 85 and entails a rather large increase in entropy (Δ H ° = 9.00 kcal/mol and Δ S ° = 16.3 cal/K/mol; K eq = 4.4 at 400 °C). , The extreme crowding of the bulky pentafluoroethyl groups in the benzene is relieved when the molecule folds up into the roof-shaped Dewar structure, with an accompanying increase in degrees of freedom. …”
Section: Fluorocarbons Vs Hydrocarbons: Contrasts In
Reactivitymentioning
Fluorocarbons, organic molecules with carbon skeletons and fluorine "skins", differ fundamentally from their hydrocarbon counterparts in interesting and useful ways. A selection of the myriad applications fluorocarbons and their derivatives have found in modern life is described and related to molecular properties. Salient aspects of the nature and reactivity of fluorocarbon compounds are highlighted by comparison with their more familiar hydrocarbon analogues.
“…When perfluorohexaethyl benzene ( 87 ) vapor is subjected to low-pressure pyrolysis at 400 °C, it is transformed into its Dewar isomer 86 . This very remarkable reaction occurs because it is 50 kcal/mol less endothermic than the formation of 84 from 85 and entails a rather large increase in entropy (Δ H ° = 9.00 kcal/mol and Δ S ° = 16.3 cal/K/mol; K eq = 4.4 at 400 °C). , The extreme crowding of the bulky pentafluoroethyl groups in the benzene is relieved when the molecule folds up into the roof-shaped Dewar structure, with an accompanying increase in degrees of freedom. …”
Section: Fluorocarbons Vs Hydrocarbons: Contrasts In
Reactivitymentioning
Fluorocarbons, organic molecules with carbon skeletons and fluorine "skins", differ fundamentally from their hydrocarbon counterparts in interesting and useful ways. A selection of the myriad applications fluorocarbons and their derivatives have found in modern life is described and related to molecular properties. Salient aspects of the nature and reactivity of fluorocarbon compounds are highlighted by comparison with their more familiar hydrocarbon analogues.
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