Some Geometric and Electronic Structural Effects of Perfluorinating Propionyl Chloride

Propionyl chloride and perfluoropropionyl chloride have been characterized using chirped pulse Fourier transform microwave spectroscopy between the frequency range of 8 and 14 GHz. Molecules were studied in separate experiments in supersonic expansions of argon. The 35Cl, 37Cl, and each of the monoisotopic 13C substituted isotopologues of propionyl chloride were observed. The 35Cl and 37Cl isotopologues of perfluoropropionyl chloride were observed. Analyses of the resulting microwave spectra have yielded spectroscopic constants for the target molecules. The analyses indicate that, under the conditions of these experiments, both molecules are only detectable as cis conformers in which ∠CCCO = 0°. Comparisons are made between the electronic and geometric structure of propionyl chloride and perfluoropropionyl chloride, and also other acyl chlorides. The data produced are relevant in regards to quantifying the known destabilizing effect of perfluoroalky chains on carbonyl groups. Distinct differences in electronegativity between the CH3CH2CO− and CF3CF2CO− groups are discussed. Methyl group internal rotation is observed for propionyl chloride and has been analyzed to produce a V3 barrier height.