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 ${\mu }_a\text{\hspace{0.17em}=\hspace{0.17em}0.38\hspace{0.17em}±\hspace{0.17em}0.02}\mathrm{D}{\mathrm{,\; \mu }}_b\text{\hspace{0.17em}=\hspace{0.17em}1.47\hspace{0.17em}±\hspace{0.17em}0.01}\mathrm{D}$ , and ${\mu }_c\text{\hspace{0.17em}≈\hspace{0.17em}0.0}\mathrm{D}$ ; 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.