Knowledge Bank

The 2-fluoroethanol (FE) monomer has five conformers and exists predominately in the all-{\em gauch} conformation which is stabilized by an intra-molecular O-H$\mathrm{<mrow\; data-mjx-texclass="ORD">...</mrow>}$F bond. When interacting with another molecule through hydrogen bonding, FE exhibits transient chirality.} In this study, we examine the competition between the intra- and inter-molecular hydrogen bonds when two FE form a dimer using rotational spectroscopy and {\em ab initio} calculations. Three pairs of the homo- and heterochiral binary conformations are predicted to be local minima at the MP2/aug-ccpVTZ//MP2/6-311++G(d,p) level of theory. Jet-cooled rotational spectra of the four out of six binary conformers were measured and unambiguously assigned for the first time. All four observed binary conformers are in the {\em compact} conformation, where two binding subunits have large contact area. The four conformers have very similar binding energies. These observations are in agreement with the previous jet-cooled low resolution infrared study by Suhm and co-workers.} The FE trimers, on the other hand, show strong preference for the homochiral trimers where FEs can form cooperative O-H$\mathrm{<mrow\; data-mjx-texclass="ORD">...</mrow>}$O and C-H$\mathrm{<mrow\; data-mjx-texclass="ORD">...</mrow>}$F rings. {\em Ab initio} calculation shows that the C$3$ symmetric trimer of the all-{\em gauch} conformation is the most stable form. The comparison between the binary and ternary FE systems will be discussed.