Microwave Spectrum and Intramolecular Hydrogen Bonding in 2-Fluoroethanol

The microwave spectra of two isotopic species of 2-fluoroethanol (FCH2CH2OH and FCH2CH2OD) have been analyzed to yield some information about a proposed intramolecular hydrogen bond in the molecule. A molecular structure has been derived which reveals that the most stable rotamer is that which allows close approach of fluorine and hydrogen atoms. The F···H distance is 2.42 ± 0.02 Å; the dihedral angle FCCO is 62°12′ ± 1.0°, and the dihedral angle CCOH is 55°30′ ± 3°. The dipole moment components are μa = 0.38 ± 0.02 D, μb = 1.47 ± 0.01 D, and μc ≈ 0.0 D; these are consistent with bond moment calculations. A vibrational state attributed to the CC torsional motion has been assigned and determined to be 152 ± 10 cm−1 above the ground state. Our results suggest a hydrogen–fluorine interaction which does not grossly distort the normal molecular charge distribution.