Matrix isolation FT-IR and theoretical DFT/B3LYP spectrum of 1-Naphthol

The FT-IR spectrum of 1-Naphthol isolated in an argon matrix is performed and compared to the infrared spectra calculated at the DFT (B3LYP)/6-31+G(d) level for cis-1-Naphthol and trans-1-Naphthol rotamers in order to clarify the existence of both rotamers in the standard temperature. Comparison of the computed and the experimental matrix spectra reveals the presence in 1-Naphthol argon matrices in the standard temperature of both cis and trans rotameric forms of 1-Naphthol, the last predominating. The relative stability of the trans-1-Naphthol rotamer has also been supported by a fit comparison between the difference of predicted total energy (ETC) of both rotamers of 0.00195 a.u. corresponding to 5.12 kJ mol−1 and the variation of the standard free Gibbs energy of rotamerization (ΔGr°ΔGr°) of 5.06 kJ mol−1.Almost all 51 active vibrational modes of 1-Naphthol have been assigned. The stretching vibration of the OH group (νOH) appears to be the unique vibrational mode distinguishing the cis-1-NpOH rotamer from the trans-1-NpOH rotamer in FT-IR spectrum.

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► Observation in argon matrix of both cis and trans rotameric forms of 1-Naphthol.
► Predominance of trans rotameric over cis rotameric form in argon matrix.
► The rotameric equilibrium constant around 0.13 was calculated from experimental IR spectra.
► Assignation of all IR active vibrational modes of 1-Naphtol isomer.