Electronic structure and absorption spectra of acetylacetone and its analogs

The molecules of acetylacetone, benzoylacetone, dibenzoylmethane, and thiodibenzoylmethane have been calculated by the simple MO LCAO method and their absorption spectra recorded. The chelation of acetylacetone with a hydrogen atom does not affect the energy of the first allowed transition ¹A₁-¹B₁. Calculations correctly predict the change in the energy for this transition in the -diketone series: acetylacetone > benzoylacetone > dibenzoylmethane > thiodibenzoylmethane; the intensity reaches a maximum value for dibenzoylmethane and dropping sharply for thiodibenzoylmethane. The secondary absorption bands for benzoylacetone and dibenzoylmethane are examined experimentally and interpreted theoretically.