Structure, Tautomeric, and intramolecular hydrogen bond of Difluorobenzoylacetone; IR, UV, NMR, and quantum calculation studies

Abstract

The molecular structure, tautomerism, spectroscopy properties, and intramolecular hydrogen bonding of 4,4-difluoro-1-phenyl-1,3-butanedione, also known as difluorobenzoylacetone (DFBA), have all been analyzed using density functional theory (DFT) calculations and spectroscopic techniques (IR, UV, and NMR). The results were compared with previously reported values for trifluorobenzoylacetone (TFBA) and benzoylacetone (BA). The energy difference between the two stable cis-enol forms,calculated at the B3LYP/6–311++G** level, is 0.96 kcal/mol.Therefore, the coexistence of both forms in comparable ratios is possible, as revealed by comparing the calculated and experimental vibrational band frequencies and their intensities. Furthermore,various computational methods were employed to examine the intramolecular hydrogen bond (IHB) strength and molecular stability,including geometry, atoms in molecules (AIM), and natural bond orbitals (NBO) theories. The hydrogen bond strength of DFBA falls between that of BA and TFBA, beinggreater than TFBA but lower than BA. Transition state study show that tautomerism between both forms occurs via the proton transfer.