Matrix-isolation infrared spectroscopy of 2,3-, 2,4-, 2,5- and 3,4-difluorobenzaldehydes

► 2,3-, 2,4-, 2,5- and 3,4-Difluorobenzaldehydes have been investigated with matrix-isolation infrared spectroscopy combined with UV irradiation. ► Two rotamers (anti and syn) were identified and the observed infrared bands of each rotamer have been separated. ► The energy differences between the anti and syn rotamers have been evaluated, which agree well with those obtained by the DFT calculations.