Medium effect on the rotational isomerism in 1,3,5-triacetylbenzene

The optimal geometries, energies, polarities, infrared frequencies, and intensities of the non-polar and polar conformers of 1,3,5-triacetylbenzene were calculated using DFT/B3LYP/6-311G**and semi-empirical (AM1 and PM3) methods. All the methods revealed that the non-polar conformer prevails in vacuum. The infrared spectra in the solid state, in Ar matrix, and in liquid solutions as well as the dipole moments of 1,3,5-triacetylbenzene in many solvents show the distinct influence of the environment on the non-polar conformer ⇌ polar conformer equilibrium. The effect of solvent polarity on the standard Gibbs energy of this conformational equilibrium is quantitatively discussed in terms of the continuum-homogenous dielectric model.