Theoretical study of substituent and solvent effects on the thermodynamics for cis/trans isomerization and intramolecular rearrangements of 2,2′-diphenoquinones

Abstract

, Gibbs free energies (D isom G (g) o ), and equilibrium constants (log K isom ) for the trans ? cis isomerization of various 3,3 0 -, 4,4 0 -, and 5,5 0 -disubstituted 2,2 0 -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 0 -diphenoquinones is predicted to be more thermodynamically stable than the cis configuration, with log K isom 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 K isom by up to 5.1 units relative to the gas phase. In polar protic and polar aprotic solvents, the estimated log K isom 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 0 -diphenoquinones participating in the thermal transformation of trans-2,2 0 -diphenoquinones to oxepino [2,3-b]benzofurans. With limited exceptions for some amino derivatives, the cis-2,2 0 -diphenoquinone to oxepino [2,3-b]benzofuran isomerization is expected to be thermodynamically favorable for all substituents/phases under consideration. The cis-2,2 0 -diphenoquinone to oxepino [2,3-b]benzofuran rearrangement is predicted to become less thermodynamically favored with increasing solvent polarity/proticity.

Development of 3,5-Di-tert-butylphenol as a Model Substrate for Biomimetic Aerobic Copper Catalysis

“…5g The occurrence of oxepinobenzofurans related to 7 as a product of metal-mediated phenol oxidation can be traced to the earliest work of Müller and coworkers in 1961, 18 who originally assigned its structure as benzoxete 7′. This structure has persisted in the literature, 2a despite a structural reassignment by Hitchcock in 1978, 19 and others based on theoretical calculations, 20 or spectroscopic data. 21 We present here an X-ray structure for 7, along with phenyl-substituted derivative 7a (Scheme 3, b), 22 which substantiates Meier's structural revision, as well as the detailed characterization conducted in 2013 by Limberg.…”

Interplay of thermochemistry and Structural Chemistry, the Journal (volume 22, 2011, issues 1–3) and the discipline

“…Computational methods at different levels have been used by Rayne and Forest [167] to study substituent and solvent effects on cis/trans isomerization equilibrium of 2,2 0 -diphenoquinones and to investigate the thermodynamics of their intramolecular rearrangement. With log K isom ranging from -2.8 to -7.0, the trans configuration is lower in energy than the cis isomer.…”