Vibrational Signatures of Chirality Recognition Between α-Pinene and Alcohols for Theory Benchmarking.

ABSTRACT

Chirality recognition between largely rigid molecules can be applied as a benchmark for the description of intermolecular forces by theoretical methods, because one constituent is merely mirrored, so other deficits of the methods such as neglect of anharmonicity should mostly cancel. To test this approach, mixed OH⋅⋅⋅π-bridged dimers between the enantiomers of the bicyclic monoterpene α-pinene and the chiral secondary alcohols borneol, α-fenchol, isopinocampheol, and 1-phenylethanol were formed in a supersonic jet and probed by linear FTIR spectroscopy. With borneol and α-fenchol, pronounced shifts in the hydroxyl stretching frequencies upon exchange of the handedness are observed. From three tested density functionals, only B3LYP-D3(BJ) is able to predict these diastereomeric shifts in a satisfactory manner, while M06-2X and ωB97X-D fall short.