Fluorination effects probed in 4-fluoroacetophenone and its monohydrate

Rotational spectra of the 4-fluoroacetophenone monomer and its monohydrate were investigated by Fourier transform microwave spectroscopy complemented with quantum chemical calculations. One conformer of 4-fluoroacetophenone and two isomers of 4-fluoroacetophenone-H2O have been observed in the pulsed jets. The observation of all mono-substituted 13C isotopologues in natural abundance allows an accurate structural determination of the 4-fluoroacetophenone monomer. Both detected isomers of 4-fluoroacetophenone-H2O are stabilized by a dominant O-HMIDLINE HORIZONTAL ELLIPSISO and a secondary C-HMIDLINE HORIZONTAL ELLIPSISO hydrogen bond. The fluorination effects on the geometries, intermolecular non-covalent interactions and V3 barrier of the methyl internal rotation were analysed. The relative population ratio of the two observed isomers for 4-fluoroacetophenone-H2O was also estimated to be NI/NII approximate to 7/1. One conformer of 4-fluoroacetophenone and two isomers of 4-fluoroacetophenone-H2O were observed. Fluorination effects on geometry, internal rotation of methyl group, and non-covalent interactions were analyzed.