The enol forms of the beta-diketones, benzoylacetones, have been studied using long-range carbon-hydrogen couplings involving the chelate OH proton, O1H chemical shifts, 13C chemical shifts and deuterium isotope effects on 13C chemical shifts. Studies were done in the temperature range from 268 to 181 K. The compounds are shown to be tautomeric, in opposition to a more symmetrical, delocalised, close to one-potential well structure as found in the solid at very low temperature. The same is true for dibenzoylmethane. The isotope effects on chemical shifts are very sensitive gauges of structure in these almost symmetrical systems. Equilibrium constants are determined and related to other similar compounds.

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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.

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