Effect of Media on the Properties of Monoterpene Cyclic Eucalyptol

Abstract

Structural, electronic, topological and vibrational propertiesof Eucalyptol have been theoretically studied in the gas phaseand in acetone, chloroform, ethanol, and water solutions byusing the hybrid B3LYP/6-31G* level of theory. Theproperties were evaluated in function of the solvent´spermittivities. A higher dipole moment and lower volumevalues were observed for eucalyptol in water due probably tothe higher permittivity. Also, higher corrected solvationenergy is predicted for eucalyptol in water (-22.51 kJ/mol) inagreement with the higher volume contraction observed inthis medium (-0.4 Å3). Atomic charges reveal the mostnegative values on the O atoms and the most positive valueson the C3 and C4 atoms. MEP surfaces of eucalyptol in allmedia evidence clear nucleophilic sites on the O atoms. NBO analyses show two E→* and ELP→* transitions while theAIM studies reveal two new H---H interactions which supportvisibly the stabilities of eucalyptol in all studied media. Thegap values show a decreasing in the reactivity of eucalyptol ingas phase and mainly in chloroform and acetone solutionswhile in aqueous solution eucalyptol is slightly most reactive.Besides, the higher nucleophilic indexes of eucalyptol in allsolvents support the characteristic nucleophilic of eucalyptol,as compared with scopolamine and tropane alkaloids. Theharmonic force fields and their complete vibrationalassignments of 81 normal vibration modes were performed.The predicted IR, ATR, Raman, 1H- and 13C-NMR and UVvisiblespectra show reasonable concordance with thecorresponding experimental ones.