Abstract
It is found that aza-imino tautomerism (a ⇆ b) of the inverted porphyrinoids and its mechanism are, along with the stability of tautomeric forms in the Solv–B system, determined by the nature of a base B and the polarity of a solvent Solv. It is shown that the transition from the C6H6–B system to MeCN–B is characterized by an approximate doubling of stability constants KT of the imine form (b), and by a change of the number of molecules B involved in the process (from two to one). According to quantum-chemical data (DFT, B3LYP, CC-pVDZ) and the results from spectral measurements (electronic absorption spectra, EAS), the stability of tautomer b (imino form) falls in the series of solvents DMF > Py ~ Et2NH > MeCN > Me2CO, and tautomer a is to a lesser extent stabilized in the given media by electron donors through the formation of hydrogen bonds (except for Me2CO: DMF > Py ≫ Me2CO ≫ MeCN, Et2NH).
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