A comparative DFT study of N‑methyl‑2‑pyrrolidone: Infrared vibrational characterization, frontier electronic properties, and global reactivity descriptors

This comprehensive theoretical study addresses significant gaps in the characterization of N-methyl-2-pyrrolidone, a dipolar aprotic solvent of industrial and fundamental importance. By employing advanced density functional theory (DFT) for structural, vibrational, and electronic analyses, this study presents a systematic multi-level comparison across six distinct computational methodologies. These include the hybrid functional B3LYP paired with the 6‑31 G*, 6‑311 G**, and 6‑311 + G** basis sets, and the dispersion‑corrected range-separated functional ωB97X‑D paired with the same basis sets. The results show that the ωB97X‑D functional, particularly with the extended 6‑311 + G** basis set, provides the best overall agreement among the methods tested for predicting key molecular properties. It accurately reproduces the characteristic amide I band (ν(C O) ≈ 1651 cm −1 ) and provides a more stable and realistic description of the frontier orbitals. Detailed vibrational assignments supported by normal mode visualizations and full theoretical spectra clarify the complex infrared signature. The derived global reactivity descriptors (chemical hardness η = 5.222 eV and electronegativity χ = 3.576 eV) consistently portray NMP as a polar and electronically stable species. The electrophilicity index (ω = 1.224 eV) is reported for comparative purposes among the six DFT methods, although its interpretation as a true thermodynamic stabilization energy is precluded by the predominantly negative electron affinities obtained for the gas-phase NMP anion (with only a marginal positive value at B3LYP/6–311 +G**), consistent with its general instability as a ground-state species. Conducted via the integrated ChemCompute platform, this approach ensures full reproducibility from geometry optimization to the interactive visualization. The generated dataset constitutes a robust, methodologically benchmarked reference for the scientific and industrial communities, facilitating the identification, quality control, and predictive modeling of N-methyl-2-pyrrolidone in applications ranging from materials science to green chemistry.