Fluorination effects probed in 4-fluoroacetophenone and its monohydrate

Abstract

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–H⋯O and a secondary C–H⋯O 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 N_I/N_II ≈ 7/1.