Publication: Theoretical study of substituent and solvent effects on the thermodynamics for cis/trans isomerization and intramolecular rearrangements of 2,2'-diphenoquinones
All || By Area || By Year| Title | Theoretical study of substituent and solvent effects on the thermodynamics for cis/trans isomerization and intramolecular rearrangements of 2,2'-diphenoquinones | Authors/Editors* | S Rayne, K Forest |
|---|---|
| Where published* | Structural Chemistry |
| How published* | Journal |
| Year* | 2011 |
| Volume | 22 |
| Number | |
| Pages | 615-625 |
| Publisher | Springer |
| Keywords | 2,2'-diphenoquinones, cis/trans isomerization, intramolecular rearrangements, equilibrium constants, substituent and solvent effects, theoretical study |
| Link | http://www.springerlink.com/content/305r4252l727153v/ |
| Abstract |
Enthalpies (ÎisomH°(g)), Gibbs free energies (ÎisomG°(g)), and equilibrium constants (log Kisom) for the transâcis isomerization of various 3,3'-, 4,4'-, and 5,5'- disubstituted 2,2'-diphenoquinones with a range of electron withdrawing and releasing moieties (methyl, fluoro, chloro, bromo, trifluoromethyl, and amino) were calculated in the gas phase and in the solvent phase (n-hexane, benzene, n-octanol, acetonitrile, and water). In the gas phase, the trans isomer of the parent and all substituted 2,2'-diphenoquinones is predicted to be more thermodynamically stable than the cis configuration, with log Kisom ranging from -2.8 to -7.0. For all compounds, increasing solvent polarity/proticity progressively favors shifting the cis/trans equilibrium towards greater contributions of the cis configuration and substantially increases the log Kisom by up to 5.1 units relative to the gas phase. In polar protic and polar aprotic solvents, the estimated log Kisom ranges as low as -0.4, indicating significant populations of the cis isomers should be present. The findings support the polar solvent phase mechanistic predictions for a cis configuration of 2,2'-diphenoquinones participating in the thermal transformation of trans 2,2'-diphenoquinones to oxepino[2,3-b]benzofurans. With limited exceptions for some amino derivatives, the cis-2,2'-diphenoquinone to oxepino[2,3-b]benzofuran isomerization is expected to be thermodynamically favorable for all substituents/phases under consideration. The cis-2,2'-diphenoquinone to oxepino[2,3-b]benzofuran rearrangement is predicted to become less thermodynamically favored with increasing solvent polarity/proticity. |
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