The Effects of Substituents and Solvents on the Conformation of Benzophenones

Athena Mantas, Sonia Blanco, Ferdinando Ferretti
2003 Internet Electronic Journal of Molecular Design   unpublished
Motivation. Natural and synthetic benzophenones are compounds of great scientific and applied interest due to the varied biological and physicochemical properties that they posses. As part of a program aimed at investigating new physicochemical properties of substituted benzophenones, we carry out a study on the influence of the substituents and solvents upon the molecular conformations of these compounds. In the future, we expect to propose relationships between the molecular structural
more » ... r structural parameters with diverse experimental properties of the compounds that are currently being determined in our laboratory. Method. Basis sets at the HF/6-31G(d) and B3LYP/6-31G(d) levels of theory were used for calculations. Onsager's and Tomasi's methods were used to analyze the solvent effects on the nine benzophenones studied. Results. A conformational equilibrium was proposed between the two conformers of benzophenones with the greatest thermodynamic stability. The total energies, torsional angles, dipole moments, structural and reactivity molecular parameters, and conformational equilibrium constants were calculated in vacuum, ethanol, methanol and water. The calculated magnitudes were correlated with Hammett's substituent constants and parameters of solvating solvents. Conclusions. The benzophenones investigated possess non-planar structures. Very good linear relationships between the molecular dihedral angles and Hammett's p-substituent constants were obtained. The electron-donating substituents increase the planarity of the substituted benzoyl group that involves phenyl ring A of the molecules, as well as the folding of phenyl ring B. The conformational equilibrium constants of o-hydroxy-benzophenones ranged approximately between 10-7-10-6. On the other hand, it was concluded that greater HBD capability of a solvent increases the polarization of the compounds and consequently, increases their DMs. It was further concluded that the electron-donating groups increase the strength of the IHB and that in the solvents used the o-hydroxy-benzophenones possess an important IHB of the moderate class. Availability.
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