Hydrogen bond interactions between thioethers and amides: A joint rotational spectroscopic and theoretical study of the formamide...dimethyl sulfide adduct

The rotational spectrum of the binary adduct of formamide (HCONH2) with dimethyl sulfide (DMS) has been investigated employing cavity-based Fourier transform microwave spectroscopy combined with theoretical computations. Experimentally, only one isomer of the adduct was unambiguously observed and assigned according to the theoretically predicted spectroscopic parameters, and its rotational spectrum displays the hyperfine splittings associated with the N-14 nuclear quadrupole coupling effect. The observed isomer exhibits C s symmetry, such that the LCSC angle of the DMS subunit is bisected by the ab-plane of the HCONH2 moiety. The two moieties in the detected isomer are connected via one primary N-H center dot center dot center dot S and two secondary C-H center dot center dot center dot O hydrogen bonds. Quantum theory of atoms in molecules (QTAIM), non-covalent interaction (NCI), natural bond orbital (NBO) and symmetry-adapted perturbation theory (SAPT) approaches were utilized for characterizing the intermolecular interactions occurring in the titled adduct. Additionally, the adduct of HCONH2 with dimethyl ether (DME) was also theoretically investigated to compare the difference in structure and energy characteristics between the N-H center dot center dot center dot S and N-H center dot center dot center dot O hydrogen bonds.