DFT study of the molecular structure of 4,6-diaryl-2-oxo-1,2,3,4-tetrahydropyrimidines

Abstract

Density functional theory at the B3LYP/6–31++G(d,p) level was applied to study structural, electronic and bonding characteristics of various 5-unsubstituted 4,6-diaryl-2-oxo-1,2,3,4-tetrahydropyrimidines (THPMs). To elucidate the steric and electronic effects of the substituents on the characteristic parameters obtained from the optimized structures, additional electron-donating and electron-withdrawing substituents were considered to be at different aryl positions, which are already located on the C4 and C6 positions of the heterocyclic ring. Results of this study show that the six-membered heterocyclic ring in half of these compounds adopts a pseudo-boat conformation with a pseudo-axial orientation of the C4–aryl substituent; in other cases a twisted chair conformation is observed. The extent of deviation of the N1 and C4 atoms from the boat plane depends on the type and position of the additional substituent on both aryl rings. Dihedral angle scanning elucidates the intramolecular interaction regarding the steric and electronic effects of the additional substituent, and its location on the aryl groups at the C4 and C6 positions on the total energy content of the molecule.