We used jet-cooled broadband rotational spectroscopy to explore the balance between π-stacking and hydrogen-bonding interactions in the self-aggregation of thiophenol. Two different isomers were detected for the thiophenol dimer, revealing dispersion-controlled π-stacked structures anchored by a long S–H···S sulfur hydrogen bond. The weak intermolecular forces allow for noticeable internal dynamics in the dimers, as tunneling splittings are observed for the global minimum. The large-amplitude motion is ascribed to a concerted inversion motion between the two rings, exchanging the roles of the proton donor and acceptor in the thiol groups. The determined torsional barrier of B₂ = 250.3 cm^–1 is consistent with theoretical predictions (290–502 cm^–1) and the monomer barrier of 277.1(3) cm^–1. For the thiophenol trimer, a symmetric top structure was assigned in the spectrum. The results highlight the relevance of substituent effects to modulate π-stacking geometries and the role of the sulfur-centered hydrogen bonds.

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 ΔE₀₊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 cm⁻¹. 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 ΔE₀₊₀₋ = 32.7(4) GHz and the potential barrier in the complex increases to B₂ = 494 cm⁻¹.

The monohydrates of thenyl alcohol and thenyl mercaptan have been probed in a supersonic jet expansion using chirped-pulse and Fabry–Perot Fourier-transform microwave spectroscopy. The rotational spectra revealed a single isomer for each of the dimers. The thenyl alcohol hydrate is stabilized by an O–H⋯O_w hydrogen bond between the alcohol and water, with water acting as a proton acceptor and additionally engaging in an O_w–H⋯π interaction with the thenyl ring. Conversely, water behaves as a proton donor in the thenyl mercaptan hydrate, linking to the thiol group though an O_w–H⋯S hydrogen bond and secondary O_w–H⋯π interactions with the ring. In both dimers water retains internal mobility, as tunneling doublings in the spectrum confirm an internal rotation motion of water inside the cluster. The experimental results have been complemented with density-functional-theory molecular orbital calculations, binding energy decomposition and a topological analysis of the electronic density, providing a comparative description of the effects of hydrogen bonding of water to the alcohol and thiol groups in the dimers, relevant to understand hydrogen bonding to sulfur centers.