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°) 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.

Infrared spectra of proton transfer complexes of the cycleanine alkaloid in solid state.

Proton transfer complexes obtained between the cycleanine alkaloid and hydrogen chloride, hydrogen bromide and nitric acids have been investigated by infrared spectroscopic technique between 4000 and 400 cm(-1) in KBr. The vibrational perturbations brought about by proton transfer complex formation, discussed in terms of preferred site of interaction, show that the proton of the inorganic acids is transferred to cycleanine through one of its N sites.

Infrared spectra of 6-thioguanine tautomers. An experimental and theoretical approach.

Both amino-thiol N9H and amino-thiol N7H tautomeric forms of 6-thioguanine have been identified in approximately equal abundance in infrared studies of these molecules isolated in the hydrophobic environment of an argon matrix at 12 K. The relative concentrations of the amino-thiol N9H and amino-thiol N7H ([SH, N9H]/[SH, N7H] = K(N9H-N7H) = 1.00 +/- 0.02) are estimated from the observed relative infrared absorbances. From these relative concentrations, the difference in the Gibbs free energy of these two tautomers (deltaG500(N9H-N7H) = -0.012 +/- 0.005 kJ mol(-1) have been estimated. The infrared and Raman spectra of 6-thioguanine in solid state are also discussed in terms of hydrogen bonding and stacking interactions in the crystal which are not considered in the calculation. In an effort to interpret the experimental results, ab initio calculation of the infrared spectrum has been made for the amino-thione N7H tautomer at 3-21G level. Comparison with experimental spectra is of some help in the assignment of the infrared and Raman spectra for 6-thioguanine in the solid state.