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Internet Electronic Journal of Molecular Design - IEJMD, ISSN 1538-6414, CODEN IEJMAT
| ABSTRACT - Internet Electron. J. Mol. Des. July 2004, Volume 3, Number 7, 387-399 |
The Effects of Substituents and Solvents on the Conformation
of Benzophenones
Athena Mantas, Sonia E. Blanco, and Ferdinando H. Ferretti
Internet Electron. J. Mol. Des. 2004, 3, 387-399
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Abstract:
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
parameters with diverse experimental properties of the
compounds that are currently being determined in our laboratory.
The HF/6-31G(d) and B3LYP/6-31G(d) methods were used for
calculations. Onsager's and Tomasi's models were used to
analyze the solvent effects on the nine benzophenones studied. 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. The benzophenones investigated have
non-planar structures. Very good linear relationships between the
molecular dihedral angles and Hammett's p-substituent constants
were obtained. 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 hydrogen-bond donor
capability of a solvent increases the polarization of the
compounds and consequently, increases their dipole moments. It
was further concluded that the electron-donating groups increase
the strength of the intramolecular hydrogen bond and that in the
solvents used the o-hydroxy-benzophenones possess an
important intramolecular hydrogen bond of the moderate class.
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