Lock‐and‐Key Principle on a Microscopic Scale: The Case of the Propylene Oxide⋅⋅⋅Ethanol Complex

Molecular recognition : The binding between propylene oxide (PO) and ethanol resembles the lock‐and‐key principle, with ( R )‐PO as a rigid lock and G −, G +, and T  conformers of EtOH as different keys (see picture; C yellow, O red). Six hydrogen‐bonded PO⋅⋅⋅EtOH conformers were studied using rotational spectroscopy and ab initio calculations, revealing which EtOH key fits best into the PO lock.