Infrared spectra and photodecomposition of benzohydroxamic acid isolated in argon matrices

The structure and spectra of the benzohydroxamic acid (BHA) molecule were studied by matrix isolation FT-IR spectroscopy and molecular orbital calculations undertaken at the MP2/6–311++G(2d,2p) level of theory. In consonance with theoretical predictions, 1Z represents the most stable keto tautomer in the gas phase, being the dominant species trapped in argon matrices, while the 2Z tautomer also contributes to the spectrum of the isolated BHA. The abundances calculated at the temperature of evaporation of BHA are equal to 80.6% and 19.2% for 1Z and 2Z tautomers of BHA, respectively, which is in consonance with the experimental relative abundance values (74.4% for 1Z and 25.6% for 2Z). The irradiation of the C6H5CONHOH/Ar matrices with the full output of the Xe arc lamp leads to the formation of the C6H5NHOH⋯CO (1) and C6H5NCO⋅⋅⋅H2O (2) complexes. The comparison of the theoretical spectra with the experimental ones allowed to determine the structures of the complexes formed in the matrix. The mechanisms of the reaction channels leading to formation of the photoproducts are proposed. It is concluded that the first step in formation of the complex (1) is the cleavage of the C–N bond, whereas the creation of the complex (2) is due to the scission of the N–O bond. •IR spectrum of isolated benzohydroxamic acid in solid argon was recorded.•1Z keto and 2Z iminol tautomers of benzohydroxamic acid were identified in the spectra.•The experimental relative abundances were equal to 74.4% for 1Z and 25.6% for 2Z.•The irradiation of isolated benzohydroxamic acid with Xe lamp led to photodecomposition.•Two main photoproducts were formed as a result of C–N or N–O bonds cleavage.