Quantum chemical and experimental study of 1,2,4-trihydroxy-para-menthane

Abstract The conformational analysis of the para -menthane ( PM ) and 1,2,4-trihydroxy- para -menthane ( TPM ) is performed using the quantum chemical density functional theory (DFT) and ab initio Moller-Plesset perturbation theory up to the second order (MP2). In TPM , three hydroxyl groups generate eight stereoisomers comparing to the four para -menthane stereoisomers. From the thermodynamics point of view, the most preferred conformations show the chair-shaped configuration of the cyclohexane ring. The obtained energy barriers for the isopropyl group rotation in the chair-shaped stereoisomers are between 35 and 45 kJ mol −1 . The crystal structure as well as the solvated TPM stereoisomer isolated from the Tea tree oil, Melaleuca alternifolia (Maiden & Betche) Cheel, were investigated experimentally. Isolated stereoisomer corresponds to the most energetically preferred conformation and the calculated structural data agree very well with the results from the X-ray and nuclear magnetic resonance measurements. Finally, the influence of the conformation and the presence of the intramolecular hydrogen bonds on the homolytic O H bond dissociation enthalpies and proton affinities were also discussed with respect to the simple alcohols (methanol, iso -propanol, iso -pentanol, tert -butanol, cyclohexanol) and phenol.