Crystal and Molecular Structures of New Chromone Derivatives as Empirical Evidence of Intramolecular Proton Transfer Reaction; Ab Initio Studies on Intramolecular H-Bonds in Enaminones

The crystal and molecular structures of two new phosphorochromones determined by single-crystal X-ray diffraction are presented. The existence of two tautomers stabilized by intramolecular N−H···O and O−H···N hydrogen bonds and environmental effects in crystals is observed as evidence of the proton transfer reaction. The proton transfer process within simple enaminones being analogues of the compounds studied by X-ray diffraction methods is investigated usingMP2/6-311++G** and MP4/6-311++G** levels of theory. The Bader theory is also applied in the analysis of the hydrogen bonding within investigated systems. The results indicate that the systems with N−H···O intramolecular hydrogen bonds are more stable than those containing O−H···N bonds.