Disentangling the complex network of non-covalent interactions in fenchone hydrates via rotational spectroscopy and quantum chemistry

Abstract

The hydrates of the monoterpenoid fenchone (C₁₀H₁₆O)·(H₂O)_n (n = 1, 2, 3) were investigated by both computational chemistry and microwave spectroscopy. Two monohydrates, three dihydrates and for the first time three trihydrates were identified through the observation of the parent and ¹⁸O isotopologues in the rotational spectrum from 2 to 20 GHz. For each hydrate, the sets of rotational constants enabled the determination of the substitution coordinates of the oxygen water atoms as well as an effective structure accounting for the arrangement of the water molecules around fenchone. The hydrates consist of water chains anchored to fenchone by a –CO⋯H–O hydrogen bond and further stabilized by numerous –H–O⋯H–C– secondary hydrogen bonds with the alkyl hydrogen atoms of fenchone.