Infrared spectra of syn and anti isomers of benzaldoxime and pyridine-4-aldoxime: An experimental matrix isolation and theoretical density functional theory study

Infrared spectra of syn and anti isomers of benzaldoxime and pyridine-4-aldoxime isolated in low-temperature Ar and N₂ matrixes are reported. The syn isomeric forms of these compounds are highly predominant in the matrixes after deposition. These forms were identified on the basis of their infrared spectra. Upon UV irradiation of the matrixes, new spectra appeared and were assigned to the anti forms of the compounds. The observed photoreactions led to photostationary states. The infrared spectra of the syn and anti isomers were separated and interpreted by comparison with the spectra theoretically calculated at the DFT(B3LYP)/6-31++G^** level. Good agreement between the experimental observations and the theoretical calculations allowed for reliable assignment of the infrared bands in the spectra of the syn and anti isomers of both compounds.