The literature data on the synthesis and chemical The literature data on the synthesis and chemical properties of fluoro-substituted properties of fluoro-substituted b b-diketones and -diketones and b b-tri--triketones are generalized. The bibliography includes 312 ketones are generalized. The bibliography includes 312 references references. .Received

The structure of benzoyldimedone was established by X-ray diffraction analysis. The only tautomer was found. In this tautomer, the enol proton is covalently bound to the oxygen atom that is remote from the phenyl group. The role of steric and electronic factors in stabilization of the enol structure is analyzed. The geometric characteristics of the ring formed through an intramolecular hydrogen bond are discussed.Key words: X-ray diffraction analysis, tautomerism, intramolecular hydrogen bond, ]3-dike/ones, [3-triketones, conjugation, 2-benzoyl-5,5-dimethylcyclohexane-1,3-dione.13-Diketones and 13-triketones attract attention of researchers t'z because of their use in synthetic practice, including the synthesis of biologically active compounds, and the presence of the keto-enol and enol-enol tautomerism. Besides, the enol tautomers of these compounds were found to have a strong intramolecular hydrogen bond. The tautomeric properties and the presence of the H bond are responsible for the high lability of the structures and high reactivities of these compounds both when substituents are introduced and when the temperature and the solvent are varied. The regularities of the influence of these factors on the enol tautomers and their structures remain in many respects unclear.NMR spectral studies demonstrated 3 that in the case of acetyldimedone, unlike acetylacetone, 2 the replacement of the methyl group by the phenyl fragment leads to a shift of the enol-enol tautomeric equilibrium toward the tautomer containing the enol proton at the O atom that is remote from the phenyl group. Previously, 4 based on the data of low-temperature neutron diffraction study, s it has been concluded that there is only one potential well for the H bond in the benzoylacetone molecule. This conclusion is inconsistent with abundant data on the structures of [3-diketones 2 and is, apparently, somewhat untimely. The structures of [3-diketones have been studied in detail by X-ray and neutron diffraction analysis. 6-13 The structures of ~-triketones have been studied only in two works. 14.t5 In this work, the structure of the benzoyldimedone molecule was studied by X-ray diffraction analysis. ExperimentalSingle crystals of 2-benzoyl-5,5-dimethylcyclohexane-1.3-dione were prepared by slow evaporation from a 1 : I ether--hexane mixture with cooling to ~10 ~ A crystal of dimensions 0.8• mm was chosen for X-ray diffraction study. The three-dimensional X-ray diffraction data set was collected on an a~ztomated four-circle Nicolet R3m diffractometer (Mo-Kct radiation, graphite monochromator. (based on all data). All calculations were carried out using the SHELX-97 program package. 16-Is The atomic coordinates, bond lengths, and bond angles of the fS-triketone were deposited with the Cambridge Structural Database.

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