PROTONATED γ-PYRONES

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Abstract
The vibrational spectra of several salts of 4-pyrone and 2,6-dimethyl-4-pyrone have been measured in the solid state. Deuterium replacement has been used to identify motions of the hydrogen atom which is located on the carbonyl oxygen atom and forms a hydrogen bond with the anion.Bands due to OH stretching vibrations have been observed from 2086 cm−1 in the HCl salt to 3310 cm−1 in the hexachloroantimonate of 2,6-dimethyl-4-pyrone. In-plane hydrogen-deformation modes of the OH group have been found near 1300 cm−1 with a much smaller range in the different salts than the stretching vibration. For the 4-pyrone salts the OH stretching vibrations were at similar frequencies, and the in-plane hydrogen-deformation frequencies were close to 1340 cm−1. Bands due to the out-of-plane deformation were not observed.Aqueous solutions of 2,6-dimethyl-4-pyrone hydrochloride at various concentrations showed the presence of both protonated and neutral molecules.