Accurate Geometry and Non‐Covalent Interactions in 1‐Phenylethanol and its Monohydrate: A Rotational Study

The pure rotational spectra of 1‐phenylethanol and its monohydrate were measured by using a pulsed jet Fourier transform microwave spectrometer. One conformer of the 1‐phenylethanol monomer with the trans form was observed in the pulsed jet. The experimental values of rotational constants of ten isotopologues, including eight mono‐substituted 13C and one D isotopologues, allow an accurate structure determination of the skeleton of 1‐phenylethanol. For its monohydrate, only one isomer has been observed, of which 1‐phenylethanol adopts the trans form and binds with water through an O−H⋅⋅⋅Ow and an Ow−H⋅⋅⋅π hydrogen bond. Each rotational transition displays a doublet with a relative intensity ratio of 1 : 3, due to a hindered internal rotation of water around its C2 axis. This study provides the information on accurate geometry of 1‐phenylethanol (PE) and large amplitude motion of water in the PE monohydrate. The rotational study of 1‐phenylethanol and its monohydrate provides an insight into the influence of sizable aromatic π moiety on the conformational structure and non‐covalent interactions of flexible ethanol derivatives.