Rotational spectrum of 2-fluoro-benzylalcohol

The rotational spectra of 2-fluoro-benzyl alcohol and of its OD isotopologue have been assigned and measured by free jet absorption millimeter wave spectroscopy. The spectrum is consistent with a gauche conformation of the oxygen atom, characterized by a OC-C1C2 dihedral angle of approximately 66°, and with the hydroxyl group zusammen with respect to the F atom, in such a way to form a OH•••F hydrogen bond. Such a configuration is twofold degenerate, corresponding to the two equivalent configurations with the OH group above and below the aromatic ring, but no tunnelling effects have been observed for the motion connecting the two equivalent minima. The entgegen conformer is expected to be stable, but its rotational spectrum has not been observed, probably because in the supersonic expansion it relaxes to the more stable zuzammen species through a quite low barrier