Quinazolin-4-yl-sulfanylacetyl-hydrazone derivatives; Synthesis, molecular structure and electronic properties

Four new acetylhydrazone derivatives of quinazoline have been synthesized and characterized. The molecular structures and relative stabilities of four possible isomers for each acetylhydrazone are calculated using DFT/B3LYP/6-31G(d,p) method. The calculations results predicted higher stability of the E-isomers compared to the Z-isomers in the gas phase. The syn-E isomer is the predominant form in gaseous phase for all the studied hydrazones except for the hydrazone derived from salicylaldehyde where the anti-E is the most stable isomer. The latter is stabilized by two strong intramolecular H-bonds instead of one in the others. The electronic and spectroscopic properties of the most stable isomers were also calculated using the same level of theory. The calculated atomic polar tensor (APT) charges indicated an increase of the positive charge density at the H-sites involved in the H-bonding interactions. The HOMO and LUMO energies are negative indicating that the compounds under investigation are stable. The electronic transition from the ground state to the excited state belongs to π–π* transition. The calculated vibrational spectra showed strong red shifts and increase in the vibrational intensity of the NH and OH stretching modes due to the intramolecular H-bonding interactions. In DMSO solution, the NMR spectra of the studied hydrazones revealed that such polar solvents stabilize the syn isomers for all the studied hydrazones except for the hydrazone derived from salicylaldehyde where the anti isomer is the major.