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Enol content, of carbonyl

Keto-Enol Tautomerism Enol Content of Carbonyl and Carboxyl Compounds... [Pg.489]

TABLE 2.1 The Enol Content of Some Carbonyl Compounds... [Pg.74]

TABLE 2.1 The enol content of some carbonyl compounds... [Pg.70]

Fig. 12.1. Substituent dependency of the enol content of aldehydes and ketones. Here, the p/CE values, i.e., the negative of the base-10 logarithm of the equilibrium constants /fE of the respective tau-tomerization carbonyl compound enol, are used as a measure. Fig. 12.1. Substituent dependency of the enol content of aldehydes and ketones. Here, the p/CE values, i.e., the negative of the base-10 logarithm of the equilibrium constants /fE of the respective tau-tomerization carbonyl compound enol, are used as a measure.
Fig. 12.2. (Mono-)carboxyl-and (mono-)carbonyl compounds, in the order of increasing enolcontent (for the enol contents of active-methylene compounds see Table 12.1.)... Fig. 12.2. (Mono-)carboxyl-and (mono-)carbonyl compounds, in the order of increasing enolcontent (for the enol contents of active-methylene compounds see Table 12.1.)...
The enol content of simple aldehydes and ketones is low under standard acid-catalyzed conditions. Silyl enol ethers, often available free of regioisomers, are an important source of enol equivalents for nucleophilic addition reactions. The reaction of silyl enol ethers with carbonyl compounds in the presence of BF3 Et20, SnCl4, TiCl4 or InCl3 proceeds through an open transition state instead of a closed transition state and leads, after hydrolytic workup, to aldol products. [Pg.243]

As Table 20.2 illustrates, the enol content of simple carbonyl compounds is quite small. Most exist almost entirely in their keto forms. Acetaldehyde contains less than 1 ppm of its enol, and acetone 100 times less than that. Each of the three simple aldehydes and ketones in the table (acetaldehyde, acetone, and 2-methylpropanal) has a single enol isomer. In many other cases stereoisomeric and constitutionally isomeric enols are possible. [Pg.896]

Properties of Sulphides.—An a-alkylthio-group increases the enol content of jS-dicarbonyl compounds,and causes a shift in carbonyl stretching frequency to lower values, in a-(alkylthio) thioesters, ketones, and amides the C—N stretching frequency in corresponding nitriles is similarly altered. ... [Pg.18]

Keto-enol tautomerism was discussed in Chapter 10 (Section 10.6) in connection with the hydration reaction of alkynes, including oxymercuration or hydroboration. The carbonyl form is more stable, and for most aldehydes and ketones only a tiny amount of enol is present. Acetone (2), for example, exists primarily as the ketone, and experiments show only 1.5 x 10 % enol. This experiment titrated acetone with diatomic bromine and measured the extent of reaction, which converted 2 to l-bromo-2-propanone (a-bromoacetone, 4). The second product in this reaction is HBr. By this experiment, the enol content of acetone—and presumably of other simple ketones—is remarkably small. [Pg.1123]

Keto enol equilibration is a property of carbonyl compounds that contain a proton on their a carbon and normally favors the keto form (Table 20.1). Simple aldehydes and ketones exist almost entirely in their keto forms acetaldehyde contains less than 1 ppm of its enol, and acetone contains 100 times less than that. The enol content of acetic acid and methyl acetate is even smaller because their keto isomers are stabilized by electron release from OH and OCH3, respectively, to C=0 the enols are not. [Pg.821]

Since fluoro-carbonyl compounds are such useful and versatile synthetic intermediates, much effort has been devoted to their preparation [124], but only in a few instances has elemental fluorine been used directly. One of the earliest successful direct fluorinations of a simple carbonyl compound was the fluorina-tion of pyruvic acid derivatives which have a high enol content (R = Aryl, Acyl) (Fig. 47) [125] in the solvent being used (mixtures of CF2C1CFC12 and acetonitrile). However, in derivatives where the enol content was low (R = Alkyl), complicated mixtures of products were obtained. [Pg.18]

The equilibrium position between a simple ketone and its enol usually lies far on the side of the ketone (see Table 17-2). However, there are some interesting and important exceptions to this generalization. For instance, the influence of two carbonyl groups on the enol content is very striking, as we can see from the fact that 85% of 2,4-pentanedione is the enol form at equilibrium ... [Pg.740]

Kinetic and thermodynamic measurements show that 2-phenylacetylthiophene (92a) has a low enol content K = 3.55 x 10 7 (or )K = 6.45).136 The keto and enol tautomers have pKa values of 14.60 and 8.15, respectively. Relative to a phenyl or furanyl substituent at the carbonyl carbon, the thiophene increases the acidity of the enol tautomer, but stabilizes the ketone, probably via the resonance contribution (92b). Thus 2-thiophenyl stabilizes the enolate by electron attraction, but the ketone by donation. Effects of micelles on the equilibria are also reported. [Pg.24]

The double bond of the enol form of 1,4-cyclohexanedione is not conjugated with the carbonyl group. Its enol content is expected to be similar to that of cyclohexanone. [Pg.479]

The bottom line complements Figure 12.1 by adding the >Ky values of representative ketones. The comparison of E G reveals the same substituent effects that are familiar from the analogous aldehydes A-C the enol content is increased by alkyl substituents in the on-position, and even more so by aryl substituents in the a-position. The ketone H in Figure 12.1, the nonexistent isophenol has by far the highest propensity to enolization of all the carbonyl compounds shown. The reason, of course, is that the tautomeric enol, phenol, is favored because of its aromaticity and thus particularly efficient C=C double bond stabilization. [Pg.490]

Most of these methods are unable to distinguish between enol and another fast-reacting species and, as stressed by Dubois and Barbier, results are highly dependent on the purity of the carbonyl compound. Another procedure which apparently does not suffer the same drawback was more recently suggested by Bell and Smith and was applied to cyclopentanone and cyclohexanone (Bell and Smith, 1966) and to acetophenone (Novak and Loudon, 1977) ketone solutions were pretreated with bromine and the enol content was measured by potentiometry after allowing the enol to form. This method was also used for determining the acidity constants of ends. [Pg.46]

Carbonyl-containing molecules, such as 1, with an a-carbon-hydrogen C(25p )-H(li) hybridized bond can exist as an enol tautomer 2, and their relative proportions depend on the relative stability of each tautomeric component (Scheme i)"4-i20 p j. saturated carbonyl-containing molecules, like 1, the amount of enol content 2 is quite low (<1% ... [Pg.412]


See other pages where Enol content, of carbonyl is mentioned: [Pg.63]    [Pg.716]    [Pg.63]    [Pg.716]    [Pg.75]    [Pg.72]    [Pg.740]    [Pg.102]    [Pg.15]    [Pg.262]    [Pg.1127]    [Pg.1152]    [Pg.628]    [Pg.41]    [Pg.336]    [Pg.1199]    [Pg.83]    [Pg.13]    [Pg.913]    [Pg.489]    [Pg.292]    [Pg.167]    [Pg.185]    [Pg.861]    [Pg.45]    [Pg.46]    [Pg.107]   


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