Experimental and theoretical studies of intramolecular hydrogen bonding in 3-hydroxytetrahydropyran: beyond AIM analysis.

The conformational preferences of 3-hydroxytetrahydropyran (1) were evaluated using infrared and nuclear magnetic resonance spectroscopic data in solvents of different polarities. Theoretical calculations in the isolated phase and including the solvent effect were performed, showing that the most stable conformations for compound 1 are those containing the substituent in the axial and equatorial orientations. The axial conformation is more stable in the isolated phase and in a nonpolar solvent, while the equatorial conformation is more stable than the axial in polar media. The occurrence of intramolecular hydrogen-bonded O-H···O in the axial conformer was detected from infrared spectra in a nonpolar solvent at different concentrations. Our attempt to evaluate this interaction using population natural bond orbital and topological quantum theory of atoms in molecules analyses failed, but topological noncovalent interaction analysis was capable of characterizing it.