Quantum-chemical and correlation study of deprotonation and complexation of 1-amino-4-hydroxyanthraquinone |
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Authors: | V Ya Fain B E Zaitsev M A Ryabov P V Strashnov |
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Institution: | 1.Russian Peoples’ Friendship University,Moscow,Russia |
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Abstract: | Existing views on the deprotonation and complexation of 1-amino-4-hydroxyanthraquinone are wrong. This compound, its anions,
and complexes with metals are not individual substances, but they form a dynamic equilibrium mixture of keto-enol (keto-oxide)
and amino-imine tautomers. Different samples of the same compound differ by the tautomeric composition, the respective information
is contained in their electron absorption spectra. In weak alkaline solutions the deprotonation occurs exclusively at the
hydroxy group. Most typical structure of 1-amino-4-hydroxyanthraquinone anions is 1,10-quinoid, its metal complexes have 9,10-and
1,10-quinoid structures. The ground states of molecules are more responsible for the tautomeric transformations than the excited
states. Quantum-chemical calculations of tautomeric anthraquinones by semiempirical PPP methods are more reliable than modern
ab initio calculations. |
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