Chiral recognition between 1-(4-fluorophenyl)ethanol and 2-butanol: higher binding energy of homochiral complexes in the gas pahse

Diastereomeric adducts between (S)-1-(4-fluorophenyl)-ethanol and R and S 2-butanol, formed by supersonic expansion, were studied by a combination of mass selected resonant two-photon ionization-spectroscopy and IR depletion spectroscopy. Chiral recognition is evidenced by the specific spectroscopic signatures of the S1 S0 electronic transition as well as different frequencies and intensities of the OH stretch vibrational mode in the ground state. D-DFT calcns. were performed to assist in the anal. of the spectra and the detn. of the structures. The homochiral and heterochiral complexes show slight structural differences, in particular in the interaction of the alkyl groups of 2-butanol with the arom. ring. The homochiral [FESBS] complex is more stable than the heterochiral [FESBR] diastereomer in both the ground and excited states. The binding energy difference was evaluated to be >0.60 kcal mol-1.