Electronic spectra and structure of 2-bromopicolines, their N-oxides, and 2-bromo-4-nitropicoline N-oxides

The UV spectra of 2-bromopicolines, their N-oxides, and 2-bromo-4-nitropicoline N-oxides are presented and the influence of substituents onλ _max andε _max of spectral bands are discussed. The electronic spectra were calculated using the modified INDO method. Transition energies, intensities, and assignments were compared with UV spectra. The degree of intramolecular CT in 2-bromopicoline N-oxides is greater than those in 2-bromopicolines and smaller than those in 2-bromo-4-nitropicoline N-oxides. The differences of the HOMO-LUMO energies indicate that the susceptibilities in the photochemical reaction lie in the order: 2-bromo-4-nitropicoline N-oxides>2-bromopicoline N-oxides>2-bromopicolines. Department of Organic Chemistry, University of Economics, PL-53 342 Wroclaw, Poland. Published in Khimiya Geterotsiklicheskikh Soedinenii, No. 2, pp. 197–207, February, 1998.