Infrared spectra of p-, m- and o-fluorobenzaldehyde in low temperature argon matrices

Three structural isomers of fluorobenzaldehyde (p-, m- and o-forms) have been investigated in detail with matrix-isolation infrared spectroscopy, in the 700–3000 cm−1 region, combined with the UV photoexcitation and the density functional calculations. Two rotamers (syn and anti) were identified for m- and o-fluorobenzaldehyde upon the photoexcitation and most of the bands of each rotamer were assigned. It is shown that the formation of the intramolecular C–H⋯F hydrogen bond for the anti rotamer of o-FB results in the shortening of the aldehyde C–H bond length and that the C–F and/or CO bond lengths are shortened for the syn rotamer of o-FB presumably due to the repulsion between the aldehyde O and F atoms.