Enol formula

It is this equilibrium which renders difficult the explanation of the course of the reactions which take place when metallic sodium or sodium ethoxide and then alkyl or acyl halide are added to these compounds. At first it was thought that the sodio compound formed with acetoacetic ester was CH3.CO.CHNa.COOC2H5, because the reaction with alkyl and acyl halides always yielded a C-derivative, CH3.CO.CHR.COOC2H5. The first example of a different course of reaction was found in the formation of an O-derivative—/3-carhethoxyhydroxycrotonic ester from sodio-acetoacetic ester and chloroformic ester (J. pr., [2], 37, 473 B., 25,1760 A., 277, 64). This could only be explained by assigning an enol formula to the sodium salt—... 

The enol (Formula 163) can be trapped by irradiating Formula 161 in the presence of dimethyl acetylenedicarboxylate (65). The adduct (Formula 164), obtained in 85% yield, is not characterized but is immediately dehydrated to the naphthalene derivative (Formula 165) (65). 

Enol formula Ethyl aceto acetate Keto formula... 

The assigning of the two types of formulas in some cases, Le.j the hydroxyl or alcohol formula (enol formula) and the ketone or carbonyl formula ketone formula), is due to the fact, not mentioned in the case of uric acid, that it is probably a tautomeric compound... 

A more eflicient and general synthetic procedure is the Masamune reaction of aldehydes with boron enolates of chiral a-silyloxy ketones. A double asymmetric induction generates two new chiral centres with enantioselectivities > 99%. It is again explained by a chair-like six-centre transition state. The repulsive interactions of the bulky cyclohexyl group with the vinylic hydrogen and the boron ligands dictate the approach of the enolate to the aldehyde (S. Masamune, 1981 A). The fi-hydroxy-x-methyl ketones obtained are pure threo products (threo = threose- or threonine-like Fischer formula also termed syn" = planar zig-zag chain with substituents on one side), and the reaction has successfully been applied to macrolide syntheses (S. Masamune, 1981 B). Optically pure threo (= syn") 8-hydroxy-a-methyl carboxylic acids are obtained by desilylation and periodate oxidation (S. Masamune, 1981 A). Chiral 0-((S)-trans-2,5-dimethyl-l-borolanyl) ketene thioketals giving pure erythro (= anti ) diastereomers have also been developed by S. Masamune (1986). 

Write a structural formula for the enol tautomer of cytosine... 

CAS name CAS Registry Number Formula X = n Bp, °C Melting point, °C Refractive index, Density at 20°C, g/L stretching frequency, max, cm Enol, %... 

The mean value of k for a large number of liquids is 2 12 liquids containing hydroxyl groups, or those which have an enolic modification, liquid chlorine, fused salts, and metals, have much smaller values of k, and this is attributed to polymerisation, since if the actual molecular weight is larger than that assumed in calculating V , the latter value will also be smaller. Ramsay and Aston (1894) assumed that it will be proportionally smaller, but the values of the polymerisation coefficients thereby deduced obviously depend on the formula assumed for the polymerised molecule, and are therefore arbitrary. 

M. Nardelli, P. Caubere, Tetrahedron Lett. 1990, 31, 7603-7606 the formula of the enol cycloadduct 7 displays the wrong orientation (personal communication from Prof. 

By their properties and reactions the phenols are very clearly distinguished from the ordinary alcohols of the aliphatic series. The fundamental difference between the two classes of compounds is that the OH-group of the phenols is attached to a doubly bound C-atom. The phenols, therefore, behave like the similarly constituted enols, as may be deduced from the following formulae ... 

Nor can there be any question of real tautomerism in the case of phenol. In its chemical properties phenol resembles the aliphatic enols in all respects. We need only recall the agreement in the acid character, the production of colour with ferric chloride, and the reactions with halogens, nitrous acid, and aromatic diazo-compounds (coupling), caused by the activity of the double bond and proceeding in the same way in phenols and aliphatic enols. The enol nature of phenol provides valuable support for the conception of the constitution of benzene as expressed in the Kekule-Thiele formula, since it is an expression of the tendency of the ring to maintain the aromatic state of lowest energy. In this connexion the hypothetical keto-form of phenol (A)—not yet obtained—would be of interest in comparison with... 

Free diethyl malonate has the constitution which corresponds to the usual formula there is no evidence for the existence of an enol-OR... 

The concept of a group is especially important in organic chemistry. A functional group represents a set of atoms that is closely linked with chemical reactivity and defined classes of substances. For instance, the functional group hydroxyl, -OH, is characteristic of the classes alcohol, phenol and enol. Alcohols are often represented by the general formula R-OH, in which R- represents a hydrocarbon group typical of aliphatic and alicyclic substances. 

It is not customary to attempt the isolation of ketone or aldehyde intermediates (121) the formula serves merely as a reminder that once hydrolysis of the protecting enol ether or acetal occurs, the same type of structure is formed from any given dicarbonyl compound. Cyclization has been carried out in refluxing ethanolic picric acid or acetic anhydride with a few drops of sulfuric acid, but Hansen and Amstutz (63JOC393) offered excellent theoretical reasons for avoiding an excess of acid, and reported that best results (Table 3) can be obtained by refluxing the dry hydrobromide in acetic anhydride containing no sulfuric acid. 

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