Prototropic processes in benzaurins. 19F and 1H NMR spectra of fluoro- and methylsubstituted 4-hydroxyphenyl-diphenylcarbinols, related fuchsones and benzaurins

Poul Erik Hansen, Alexander S. Peregudov, Dmitii N. Kravtsov, Antonina I. Krylova, Galina M. Babakhina, Ludmila S. Golovchencko, Valentina M. Pachevskaya

Research output: Contribution to journalJournal articleResearchpeer-review

Abstract

Tautomerism of benzaurins and hydration are studied. 1H and 19F chemical shifts have been determined for a number of substituted 4-hydroxyphenyl-diphenyl carbinols containing fluorine in a 3-, 3*- or 4*-position, and for similar compounds containing additional methyl groups in a position of 3, 3** or 4**. The same data have been obtained for the fuchsones prepared by dehydration of the above carbinols. On this basis chemical shifts of fluorine in different positions have been evaluated as a monitor of the transformation of 4-hydroxyphenyl group to the semiquinone moiety. The 19F NMR can be used to monitor the transformation of 4**-fluorobenzaurin and the related 3,3*-disubstituted and 3,3*,5,5*-tetramethylsubstituted compounds to the corresponding carbinols due to the addition of a water molecule and to study the tautomerism of the two latter benzaurins as well as that of 3,3*,4**trifluorobenzaurin. Furthermore, fluorine and methyl group chemical shifts are sensitive to syn-anti-isomerism in substituted fuchsones.
The prototropic process of these compounds may be slow or fast on a 1H NMR time scale depending on the solvent and may be catalyzed by water or carbonic acids. On the basis of kinetic and thermodynamic data obtained by dynamic NMR studies, a mechanism for the process has been proposed.
Original languageEnglish
JournalCentral European Journal of Chemistry
Volume9
Issue number2
Pages (from-to)253-264
Number of pages12
ISSN1895-1066
DOIs
Publication statusPublished - 2011

Keywords

  • 19F NMR
  • Prototropic tautomerism
  • Syn-anti isomerism
  • Fluoro- and methyl substituted benzaurins
  • Fuchsones

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