Rotational investigation of Biarylic Thienyl Pyridines and their Monohydrates: The role of the S···N intramolecular interaction

Abstract

We used jet-cooled broadband rotational spectroscopy and quantum mechanical calculations to study the po- tential energy surface, molecular structure and intra- and intermolecular interactions of the biarylic thienyl pyridines of 2-(2-thienyl)pyridine and 2-(2-pyridyl)benzothiophene and their monohydrates. Two isomers of the bare molecules were identified in the gas phase, characterized by planar structures and zusammen (Z) or entgegen (E) orientations around the ring junction. A single Z-isomer was observed for both monohydrates, primary stabilized by a hydroxyl-to-nitrogen (O-H⋅⋅⋅N) hydrogen bond and secondary C-H⋅⋅⋅O interactions. The compu- tational study included D3 dispersion-corrected hybrid (B3LYP) and double hybrid (B2PLYP) density functional methods, with additional calculations at the RI-MP2 and DLPNO-CCSD(T) levels. NBO calculations examined the donor-acceptor hyperconjugative effects involving the nitrogen and sulfur atoms, suggesting that their partici- pation in the larger stability of the Z form is not decisive and may involve other intramolecular interactions. In particular, examination of the electronic density shifts (EDS) further suggests that non-covalent N⋅⋅⋅S chalcogen interactions partially contribute to the preference for the Z conformation