Acetylacetone, tautomerism

Acetylacetone (2,4-pentadione) undergoes a tautomerization that can be shown as... 

For such cases in which the two forms have been brought to light solely as a result of improved experimental methods, the term tauto-merism " has been modified to desmotropism In desmotropic substances the tautomeric relations are therefore particularly clear and well defined numerous examples have become known, which now also include aceto-acetic ester. The case of acetylacetone is quite similar, but here the formation of the enol-form is much more favoured. The liquid substance contains up to 80 per cent of enol. 

The reaction of metal ion M"+ with the keto, enol tautomeric mixture of acetylacetone (acacH) in acidic aqueous solution has been treated by a similar approach to that outlined above (see Prob. 16). 

The pyridine ring system may carry snbstituents, jnst as we have seen with benzene rings. We have enconn-tered a nnmber of snch derivatives in the previons section. Hydroxy or amino heterocycles, however, may sometimes exist in tautomeric forms. We have met the concept of tantomerism primarily with carbonyl componnds, and have seen the isomerization of keto and enol tantomers (see Section 10.1). In certain cases, e.g. 1,3-dicarbonyl componnds, the enol form is a major component of the eqnilibrinm mixtnre. In the example shown, liquid acetylacetone contains about 76% of the enol tautomer. 

The potential of carbon-13 NMR in the analysis of keto-enol tautomerism has been demonstrated for 2,4-pentanedione (acetylacetone) and dimedone [293]. Quantitative evaluation of equilibrium concentrations is possible by application of the inverse gated decoupling technique illustrated in Fig. 2.23. 

In the above structure, if Ph3P is replaced by a bidentate ligand such as bipyridyl, there results a C-rj, -acetylacetonate complex in which palladium is tr-bonded to a terminal CH2 group. These presumably exist as tautomeric keto and enol forms (equation l).53... 

Watarai H, Suzuki N. Keto-enol tautomerization rates of acetylacetone in mixed aqueous media. J Inorg Nucl Chem 1974 36 1815-1829. Great Britain Pergamon Press. 

Enols The familiar tautomeric equilibrium of keto and enol forms of acetylacetone is described in Section 3.8.3.1 (see Figure 3.45). The enol form predominates over the keto form under the conditions described. 

Another nucleophilic center can also appear due to tautomerization of the unsaturated bonds induced by bases such as the fluoride ion. Thus the reaction of perfluoro-2-methylpent-2-ene with active methylene compounds, for example, acetylacetone, ethylacetoacetate, benzoylaceto-nitrile, and benzoylmethylperfluoroalkylketones in the presence of KF gives not only the products of nucleophilic substitution of fluorine... 

Propose mechanisms for the reactions shown in Problems 22-62 parts (a) and (b) and 22-63 parts (a) and (b). Pentane-2,4-dione (acetylacetone) exists as a tautomeric mixture of 8% keto and 92% enol forms. Draw the stable enol tautomer, and explain its unusual stability. 

Because of the intramolecular hydrogen bonding in the enol form of acetylacetone (2,4-pentadione), this compound tautomerizes to a great extent ... 

The synthesis of tris(acetylacetonate)chromium(III) shows additional features of this type of synthesis involving a metal compound reacting with a ligand. Acetyl acetone (2,4-pentadione), C3Hx02, undergoes a tautomerization,... 

Diketones. Beta-diketones such as acetylacetone, benzoyl-acetone, and isopropyltropolone are well known for their applications in analytical extraction of actinides. These compounds are weak acids due to tautomerization thus they can act as cation exchange extractants. Trivalent actinide [M(III)] extraction by the reagent (HA) at low aqueous acid concentration where the compound behaves both as cation exchanger and coordinator probably follows the reaction... 

A short overview of the quantum chemical and statistical physical methods of modelling the solvent effects in condensed disordered media is presented. In particular, the methods for the calculation of the electrostatic, dispersion and cavity formation contributions to the solvation energy of electroneutral solutes are considered. The calculated solvation free energies, proceeding from different geometrical shapes for the solute cavity are compared with the experimental data. The self-consistent reaction field theory has been used for a correct prediction of the tautomeric equilibrium constant of acetylacetone in different dielectric media,. Finally, solvent effects on the molecular geometry and charge distribution in condensed media are discussed. 

One of the most important applications of the quantum theory of molecules in condensed media is the prediction of their chemical reactivity. It is often necessary to predict the rate or equilibrium constant of a chemical reaction in different organic and inorganic media. However, in most cases the theoretical calculations have been limited to the aqueous solutions. Therefore, it would be important to study the applicability of the solvation theories in different dielectric media. An appropriate reaction for such study is the tautomeric equilibrium between acetylacetone (1) and its enol form (2)... 

Figure 2. AMI SCa SCRF Calculated vs. Experimental Tautomeric Equilibrium Constants logK for Acetylacetone in Different DioxaneAVater Mixtures.

Tautomerism is a combination of hydrogen-bonding and slow inter-or intra-molecular proton transfer. Jarrett et al. (1953) reported proton resonance spectra of acetylacetone (2,4-pentanedione) and 3-methyl-2,4-pentanedione. The spectra were found to be a superposition of... 

The most common j3-diketone, acetylacetone, exists in two tautomeric forms,... 

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