Effects of ring fluorination on the transient atropisomerism of benzyl alcohol: the rotational spectrum of 3,4-difluorobenzyl alcohol

The rotational spectra of the —OH and —OD isotopologues of 3,4-difluorobenzyl alcohol have been measured by pulsed jet Fourier transform microwave spectroscopy. The spectrum of one conformer has been assigned, characterised by a OCα- C1C2 dihedral angle of approximately 50◦, and with the hydroxyl group zusammen with respect to the meta-F atom. μc-type transitions of the—OH species are split into two evenly spaced component lines by 0.132(2) MHz, showing that the CH2OH group undergoes a tunnelling motion which connects two equivalent minima above and below the aromatic ring. The barrier for the interconversion of the two mirror forms has been calculated to be 155 cm−1.