Characterization of Large-Amplitude Motions and Hydrogen Bonding Interactions in the Thiophene–Water Complex by Rotational Spectroscopy
Silva, Weslley G. D. P.
van Wijngaarden, Jennifer
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The rotational fingerprint of the thiophene–water complex was investigated for the first time using Fourier transform microwave spectroscopy (7–20 GHz) aided by quantum mechanical calculations. Transitions for a single species were observed and the rotational constants for the parent and 18O isotopomers are consistent with a geometry that is highly averaged over a barrierless large amplitude motion of water that interconverts two equivalent forms corresponding to the global minimum (B2PLYP-D3(BJ)/def2-TZVP). In this effective geometry, the water lies above the thiophene ring close to its σv plane of symmetry. The observed transitions are split by a second water-centered tunneling motion that exchanges its two protons by internal rotation about its C2 axis with a calculated barrier of ~2.7 kJ mol-1 (B2PLYP-D3(BJ)/def2-TZVP). Based on quantum theory of atoms in molecules, non covalent interaction and symmetry-adapted perturbation theory analyses, the observed geometry enables two intermolecular interactions (O–H…π and O–H…S) whose electrostatic and dispersive contributions favour formation of the thiophene-water complex.