Competing hydrogen bond topologies in 2-fluoroethanol dimer

Abstract

Isolated 2-fluoroethanol exists predominantly as a pair of enantiomeric all-gauche conformations, which are stabilized by an intramolecular O-H center dot center dot center dot F interaction. Its most stable OH center dot center dot center dot OH hydrogen-bonded dimers differ in their relative monomer configuration and in their network of weak intermolecular interactions involving the electronegative fluorine atoms. OH-stretching FTIR spectra of supersonic jet expansions using He as a carrier gas reveal four dimer isomers. Only two isomers survive upon Ar admixture. Exploratory quantum chemical calculations confirm that the two surviving conformations involve insertion of the OH group of one monomer into the intramolecular O-H center dot center dot center dot F interaction of the other. The two unstable conformations consist of more loosely associated monomers. Chiral recognition leads to different OH stretching wavenumbers for homo- and heteroconfigurational dimers, but both are formed in similar quantities in the jet expansion. (c) 2005 Elsevier B.V. All rights reserved.