Solvatochromic analysis of some N-nitroso oxime derivatives – Taft and Catalan approach

Some novel N-nitroso oxime derivatives were synthesized and characterized by 1H, 13C, 1H–1H and 1H–13C COSY NMR spectra. The spectra of all these N-nitroso oximes reveal the presence of two isomers labelled as E (−NOH group is anti to N–NO moiety) and Z (−NOH group is syn to N–NO moiety) in solution and the coupling constants ruled out the possibility of normal chair conformation. From the theoretical studies and coupling constant values it was found that both E (major) and Z (minor) isomers of N-nitroso oximes exist as an equilibrium mixture of CA and boat conformation (B1) and this was also supported by DFT calculation. The photophysical properties of these oxime derivatives were studied and the observed lower fluorescence quantum yield may be due to an increase in the non-radiative deactivation rate constant. This is attributed due to the presence of non-chair conformation of N-nitroso oxime derivatives.

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• Geometrical change: equilibrium mixture of alternate chair and boat form.
• Reichardt–Dimroth solvent ET parameters: dielectric solute–solvent interactions – solvatochromic shift.
• Marcus optical dielectric solvent function: direction of excited dipole is opposite to that of the ground state-dipole.
• Lippert–Mataga plot: geometrical change takes place in the excited state.
• Taft and Catalan approach: fluorescence band shift to lower energies with increasing basicity of the solvent.