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

• Published in: Journal of molecular structure 1999-02, Vol.476 (1), p.45-55
• Main Authors: Rak, Janusz, Krzymiński, Karol, Skurski, Piotr, Jóźwiak, Ludwika, Blażejowski, Jerzy
• Format: Article
• Language: English
• Subjects: Experimental and theoretical investigations; IR–Raman spectroscopy; N-Methyl-9-acridinamines; NMR spectroscopy; Tautomerism
• ISSN: 0022-2860; 1872-8014
• DOI: 10.1016/S0022-2860(98)00530-4

Four N-methyl substituted derivatives of amino or imino forms of 9-acridinamine were synthesized and subjected to detailed IR–Raman and NMR ( 1H and 13C) investigations. Harmonic frequencies predicted at the density functional (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 forms of 9-acridinamine. Theoretical 1H and 13C chemical shifts, particularly the latter, fit the relevant NMR spectra only qualitatively; both demonstrate a unique pattern for each of the compounds studied. The derivatives examined seem to exhibit their own identity and features, reflected in unique vibrational and NMR spectra, rather than retain those of the parent tautomeric forms of 9-acridinamine. Both experimental and theoretical investigations reveal that two tautomeric forms of N-methyl-9-acridinamine, in similar to 9-acridinamine, should co-exist at room temperature. The polarity of the compounds, expressed by dipole moments, as well as distribution of relative atomic partial charges and electrostatic potential around the molecules, are unique for each of the compounds but generally similar in the groups of derivatives originating from the amino or imino tautomers of 9-acridinamine.