Study of the 3-(3,3-Dimethylbutanoyl)-4-hydroxy-6-neopentyl-2H-pyran-2-one by IR, Raman spectroscopy, and DFT

The heterocyclic structure of pyrones has a variety of biological activities and plays an important role in the creation of new drugs. Therefore, the study of the structure and spectra of pyrones is of considerable interest. In this work, the IR and Raman spectra of 3-(3,3-Dimethylbutanoyl)-4-hydroxy-6-neopentyl-2H-pyran-2-one (1) in its crystalline state was studied. The tautomerization of 1 was followed by a quantum-chemical method at the DFT/B3LYP/6-311G** level. The calculation for the 4-hydroxy enol tautomer (A) reproduces the experimental IR and Raman spectra of compound 1. The classification of the bands in the experimental vibrational spectra of 1 has been carried out. The intramolecular H-bond was characterized by IR spectroscopy. The free energies of the tautomers and their populations were calculated for two different solvents. It appears from our data that type A dominates. The content of tautomer B increases in the nonpolar solvent but does not exceed 13%. As evident from the calculations and experimental X-ray data, the pyran ring of the molecule is flat. HOMO and LUMO of molecule 1 are located on the pyran ring. During tautomeric transformations, there is a significant delocalization of charge and a change in the reactivity of the molecule. The reactivity of pyrone 1 was characterized using descriptors. The form B was found to have higher ionization energy, electron affinity, chemical potential, and electrophilic index than the A form. The dipole moment is higher for form A, and the softness of the two molecules is the same.