A theoretical and experimental study of the conformational behavior of trans-2-azidocyclohexanol in solution

Infrared spectroscopy combined with electronic structure calculations was applied to the study of the inter- and intramolecular interactions in gas phase and in solution of the racemic trans-2-azidocyclohexanol molecule and of how these interactions influence the conformational equilibrium. The diequatorial conformer is significantly favored in the equilibrium and coexists in the form of four main rotamers. Their ratio is strongly influenced by the solvent polarity. In solvents with a low relative permittivity, the dominant species depends on the compound concentration – in low concentrations the compound is in monomeric state, with an intramolecular hydrogen bond. For concentrations higher than 0.1 mol L−1, dimeric aggregates are formed. When the relative permittivity of the medium is raised, the rotamer with the greatest dipole moment is favored. Due to the orientation of the substituent groups, the rotamer interacts more strongly with the solvent. This characteristic also enables the formation of complexes with the molecules of the solvent. The analysis of the natural bond orbitals and the Wiberg bond index showed that the intensity of the hydrogen bond between the compound and the solvent is greater in tetrahydrofuran. The wavenumber of the hydrogen–oxygen bond stretching corroborates this hypothesis.