Energetics of Molecular Complexes in a Supersonic Beam: a Novel Spectroscopic Tool for Enantiomeric Discrimination

The authors report the spectroscopic detn. of the binding energy in isolated diastereomeric mol. complexes between a chiral arom. alc. [(R)-(+)-1-phenyl-1-propanol] and chiral aliph. alcs. [(R)-(-)- and (S)-(+)-2-butanol] in a supersonic beam with special regard to the dependence of the binding energy on the configuration of the chiral solvent mol. The binding energy of the diastereomeric adducts was measured using 2-color resonance 2-photon ionization expts. Some band triplets can be interpreted as due to different stable conformers. The homochiral complex is more stable than the heterochiral diastereomer in both the ground and excited states. The same is true for the corresponding ionic adducts. The difference in stability for the neutral adducts is attributed to different steric requirements.