Density functional theory and ab-initio computational study of molecular structure, tautomerism, and geometrical isomerism of ethynyl-bridged dipyridinones: In the gas phase and dielectric media

The geometries and relative stabilities for the different isomers and tautomers of ethynyl-bridged dipyridinones were calculated with full geometry optimizations using DFT method. Solvent effects have been analysed using the self-consistent reaction field theory with Onsager and continuum models for three different solvent, CHCl3, CH3OH and H2O. The geometrical parameters of all structures were almost unaffected by the solvent. Except 3a and 3b, all compounds were found to have planar structure in the gas phase and in solutions. For the 3a and 3b tautomers were observed small divergence from planarity. The keto forms were calculated considerably to be more stable than the enol forms in the gas phase and in all solutions. The differences in relative energy values between tautomers were increased in general by the effect of solvent.