IR-Raman, NMR and density functional methods in the examination of tautomerism and features of N-methyl substituted 9-acridinamine derivatives

Four N-methyl substituted derivatives of amino or imino forms of 9-acridina mine were synthesized and subjected to detailed IR-Raman and NMR (H-1 and C -13) investigations. Harmonic frequencies predicted at the density function al (DFT) level enabled certain modes to be assigned to bands in IR or Raman spectra and those characteristic of either the amino or imino tautomeric f orms of 9-acridinamine. Theoretical H-1 and C-13 chemical shifts, particula rly the latter, fit the relevant NMR spectra only qualitatively; both demon strate a unique pattern for each of the compounds studied. The derivatives examined seem to exhibit their own identity and features, reflected in uniq ue vibrational and NMR spectra, rather than retain those of the parent taut omeric forms of 9-acridinamine. Both experimental and theoretical investiga tions reveal that two tautomeric forms of N-methyl-9-acridinamine, in simil ar to 9-acridinamine, should co-exist at room temperature. The polarity of the compounds, expressed by dipole moments, as well as distribution of rela tive atomic partial charges and electrostatic potential around the molecule s, are unique for each of the compounds but generally similar in the groups of derivatives originating from the amino or imino tautomers of 9-acridina mine. (C) 1999 Elsevier Science B.V. All rights reserved.