Two conformers of cyclohexanol and the cyclohexanol–water adduct have been characterized in a jet
expansion using rotational spectroscopy. In the gas phase, cyclohexanol adopts an equatorial position
for the hydroxyl group, with the two conformers differing in the orientation of the hydroxylic hydrogen,
either gauche or trans with respect to the aliphatic hydrogen at C(1). Axial cyclohexanol was not
detected in the jet. The transitions of the gauche conformer are split into two component lines due to
the tunneling effect of the O–H internal rotation, which connects two equivalent gauche minima. The
tunneling splitting in the vibrational ground state has been determined to be DE0+0 = 52(2) GHz.
From this splitting, the inversion barriers connecting the two equivalent gauche conformers have been
determined using a flexible model to be B2 = 377 cm1. A single isomer is detected for the cyclohexanol– water dimer, in which the water molecule acts as a proton donor to the equatorial gauche ring. The presence of torsional tunneling in the adduct suggests a concerted large-amplitude-motion in which the internal rotation in the ring is accompanied by a torsion of the water molecule, to produce an equivalent enantiomer. The torsional tunneling in the adduct is reduced to DE0+0 = 32.7(4) GHz and the potential barrier in the complex increases to B2 = 494 cm1
