DFT AND HF STUDY OF STRUCTURAL, SPECTROSCOPİC, THERMOCHEMİCAL, AND ELECTRONİC PROPERTİES OF 2-ETHOXY-5-FLUORO-1H-PYRİMİDİN-4-ONE

http://doi.org/10.71284/jasem202613

Abstract

A comprehensive quantum-chemical investigation of 2-ethoxy-5-fluoro-1H-pyrimidin-4-one (C6H7FN2O2) was carried out using density functional theory (DFT) and Hartree–Fock (HF) methods at the B3LYP/6-31+G(d,p) and HF/6-31+G(d) levels to elucidate its structural, spectroscopic, thermochemical, charge distribution, and electronic properties. The optimized geometry reveals a stable heterocyclic structure in which the pyrimidinone ring, fluorine substituent, carbonyl group, and ethoxy moiety collectively govern the molecular electronic structure. The calculated geometrical parameters indicate good agreement between the theoretical approaches, confirming the reliability of the optimized molecular model. Theoretical 1H and 13C NMR chemical shifts were evaluated using the GIAO method and compared with available experimental data recorded in CDCl3. The DFT calculations reproduce the experimental chemical shifts more accurately than the HF method, highlighting the importance of electron-correlation effects in predicting magnetic shielding constants. Significant deshielding is observed for carbon atoms bonded to electronegative nitrogen, oxygen, and fluorine atoms, whereas the ethoxy-group carbons and hydrogen atoms exhibit comparatively lower chemical shifts. Atomic charge distributions were also analyzed using both Mulliken population and atomic polar tensor (APT) schemes. The results reveal pronounced electronic polarization within the molecule, with the carbonyl oxygen, fluorine atom, and pyrimidine nitrogen n atoms carrying substantial negative charge densities, while several carbon and hydrogen atoms exhibit positive charge accumulation. The calculated charge distribution confirms the existence of efficient intramolecular charge redistribution regulated by the combined electron-withdrawing effects of fluorine and carbonyl functionalities. Additionally, thermochemical calculations indicate that the molecule possesses favorable energetic stability, while the calculated dipole moment displays its polar molecular nature. Frontier molecular orbital (FMO) analysis displays that the HOMO is mainly localized over the pyrimidinone ring and heteroatom-rich regions, whereas the LUMO is concentrated around the carbonyl- and fluorine-containing portions of the heterocyclic structure. This spatial separation facilitates intramolecular charge-transfer processes. The HOMO-LUMO energy gap together with the derived global reactivity descriptors, including electronegativity, chemical hardness, softness, chemical potential, and electrophilicity index, indicate a balanced combination of electronic stability and chemical reactivity. UV-Vis spectral analysis reveals that the electronic absorption behavior is dominated by π→π* and n→π* transitions involving the conjugated heterocyclic system and heteroatom lone-pair electrons. Furthermore, electrostatic potential (ESP) and m olecular electrostatic potential (MEP) analyses identify the carbonyl oxygen atom, fluorine atom, and ring nitrogen atoms as the most electron-rich regions, while the N-H and ethoxy hydrogen atoms constitute the principal positive potential zones. All in all, the theoretical results obtained show that 2-ethoxy-5-fluoro-1H-pyrimidin-4-one possesses a highly polarized electronic structure, well-defined reactive centers, and favorable charge-transfer characteristics. The findings provide a detailed understanding of its structural stability, spectroscopic behavior, and reactivity patterns, suggesting potential relevance in pharmaceutical, agrochemical, and functional-material applications.