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Paper | Regular issue | Vol 57, No. 5, 2002, pp.895-901
Published online, 1st January, 1970
DOI: 10.3987/COM-02-9469
Ring-Chain Tautomerism of Halogenated Phenolphthaleins: Vibrational Spectroscopic and Semiempirical MO Study

Ko-ki Kunimoto,* Hiromasa Sugiura, Toshiyuki Kato, Hitoshi Senda, Akio Kuwae, and Kazuhiko Hanai

*Kanazawa University, Faculty of Technology, Department of Chemistry and Chemical Engineering, Kakuma-machi, Kanazawa 920-1192, Japan


Ring-chain tautomerism of halogenated phenolphthaleins and the effect of the halogen substitution have been studied by vibrational spectroscopic and semiempirical MO methods. The vibrational spectra indicate that the content of the colored species (carboxylate form) increases on the substitution of the isobenzofuranone ring, whereas the colorless species (lactone form) becomes dominant on the substitution of phenolic rings. MO calculations have revealed that the substitution of either ring does not change the basic property of the electronic transition of the colored species and that the relative stability of both forms is dependent on the substitution type in accord with the results of the vibrational study.