Chlorine Para-Substitution of 1-Phenylethanol: Resonant Photoionization Spectroscopy and Quantum Chemical Calculations of Hydrated and Diastereomeric Complexes.

The conformational landscape of (S)-1-(4-chlorophenyl)ethanol, its monohydrated complex, and its diastereomeric adducts with R- and S-butan-2-ol, have been investigated by resonant two-photon ionization (R2PI) spectroscopy coupled with time-of-flight mass spectrometry. Theoretical calculations at the D-B3LYP/6-31++G** level of theory have been performed to assist in the interpretation of the spectra and in the assignment of the structures. The R2PI spectra and the predicted structures have been compared with those obtained on the analogous non-halogenated and fluorinated systems, i.e., (R)-1-phenylethanol and (S)-1-(4-fluorophenyl)ethanol, respectively. It appears that the presence of chlorine atom in the para position of the aromatic ring does not influence the overall geometry of bare molecule and its complexes with respect to the non-halogenated analogous systems. Anyway, it affects the electron density in the pi system, and in turn the strength of OH···pi and CH···pi interactions. A spectral chiral discrimination is evident from the R2PI spectra of the diastereomeric adducts of (S)-1-(4-chlorophenyl)ethanol with the two enantiomers of butan-2-ol.