Conformations and non-covalent interactions of cyclohexyl isothiocyanate and its water complex.

The conformational equilibria of cyclohexyl isothiocyanate and its complex with water were studied by microwave spectroscopy combined with theoretical calculations. For the bare cyclohexyl isothiocyanate, the rotational spectra of the two conformers, namely a-trans and e-trans, were measured and analyzed. Additional mono-substituted isotopologues of two C and one S of a-trans and e-trans were also measured, which result in an accurate structural determination of the two conformers. For the binary complex with water, the rotational spectra were measured for the monohydrates of both a-trans and e-trans conformers. Water isotopologues were also detected for the monohydrates. All the measured rotational spectra show N quadrupole coupling hyperfine structures. Water molecule prefers linking to the isothiocyanate group through a OH⋯S hydrogen bond and forming two CH⋯O hydrogen bonds with the oxygen atom of water acting as a proton acceptor. The non-covalent bonding features of the monohydrates were revealed by natural bond orbital analysis and symmetry-adapted perturbation theory analysis.