Structure of flavones and flavonols. Part I: Role of substituents on the planarity of the system

In this first part of our investigation the effect of –OH, –NH2, –NO2 and other substituents on the planarity (and the level of delocalization) of a series of flavones and flavonols is assessed. This feature is particularly important with respect to the biological activity of flavonoids. The values of the dihedral angles were obtained from the optimized in gas phase and in water geometries at the density functional theory B3LYP/6-31G(d,p) level.