The tautomerism, molecular structure, and intramolecular hydrogen bonding (IHB) of 4,4,4-trifluoro-1-(2-naphthyl)- 1,3-butanedione (TF2NPT) were reinvestigated using experimental IR/UV/NMR spectroscopy supported by DFT and TD-DFT calculations in the polar and nonpolar solvents. Spectroscopic evidence shows that TF2NPT is entirely cis-enol form in the solid state and in CCl4, while only a minor diketo contribution (~2%) is observed in polar solvents by 1HNMR spectrum (CD3CN and DMSO‑d6). The UV spectrum of TF2NPT in ethanol closely resembles that of 4,4,4-trifluoro-1-phenyl-1,3-butanedione (TFBA), which exists solely in the cis-enol form, and TD-DFT results further support this configuration. Calculated relative energies in the different media and levels indicate that the diketo forms are 5.4–8.6 kcal/mol less stable than the cis-enol form, exceeding those of TFBA. According to asymmetric β-diketones, two asymmetric cis-enol tautomers (2- and 4-TF2NPT) were suggested, with the 4-form more stable by 1.0–1.5 kcal mol???? 1 (0.8–1.4 kcal/mol after ZPE correction), suggesting their coexistence. Comparison with TFBA reveals that naphthyl substitution enhances IHB strength through increased conjugation and electron delocalization. In addition, 4,4,4-trifluoro-1-(1-naphthyl)-1,3-butanedione (TF1NPT), using the reported experimental IR and NMR data, also exists exclusively as a cis-enol tautomer with comparable IHB strength.

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