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

作者：Hansen Poul Erik^*; Peregudov Alexsander S; Kravtsov Dimitrii N; Krylova Antonina I; Babakhina Galina M; Golovchenko Ludmila S; Pachevskaya Valentina M

来源：Central European Journal of Chemistry, 2011, 9(2): 253-264.

DOI：10.2478/s11532-011-0003-0

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

Tautomerism of benzaurins and hydration are studied. H-1 and F-19 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 F-19 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 H-1 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.

• 出版日期2011-4