Structural and spectral analysis of 3-and 4-methylated nitraminopyridine N-oxides

The X-ray structures of 3-methyl-2-nitraminopyridine N-oxide (3M) and 4-met hyl-2-nitraminopyridine N-oxide (4M) has been determined arid experimental electronic absorption spectra investigated. The X-ray results show that bot h compounds occur as dimers either in the molecular form (3M) or in the pro ton transferred (PT) form (4M). A `driving force' for protonation depends o n the relative position of the two monomers in the crystal lattice (paralle l for 3M and perpendicular for 4M) and on the degree of electronic conjugat ion of -NH-NO2 substituent with the pi -system of the pyridine ring. Positi on of the methyl group does not affect the direction of the CT process. Qua ntum-chemical semi-empirical PM3-CI calculations allowed an interpretation of experimental electronic absorption spectra and suggested the prototropic amino-imino equilibria which possible to occur in the solution. (C) 2001 E lsevier Science B.V. All rights reserved.