On the other hand, if an oxygen atom has a negative charge, it is called an enolate. This resonance competes with the resonance of the stabilization of the enolate resonance. The aqueous base conditions used for the aldol condensation are not suitable because the enolate anions of simple carbonyl compounds are formed in very low concentration, and hydroxide or alkoxide bases induce competing SN2 and E2 reactions of alkyl halides. Oxidative coupling of enolates, enol silanes, and enamines provides a direct method for the construction of useful 1,4‐dicarbonyl synthons. Examples of electron-withdrawing groups include the following. Because of the presence of the carbanion, it is an unstable substance. As a result, the π orbitals are parallel to the neighboring C-H bond, and the molecular structure is stabilized by weakly sharing electrons. Therefore, it cannot nucleophilic attack the carbonyl carbon. The interconversion between a carbonyl compound and its enol is known as keto-enol tautomerism. The next reaction must proceed after the enolate has been synthesized. The carbon next to the carbonyl group is called the α-carbon.

The formation of enolate ions as intermediates leads to a variety of chemical reactions. On the other hand, when a bulky strong base such as LDA is used, a proton with few substituents is easily pulled out due to steric hindrance. The reason why regioselectivity is so important in the use of enolate for alkylation is that two compounds may be formed. Although the reaction of carbonyl compounds with sodium hydride is heterogeneous and slow, sodium enolates are formed with the loss of hydrogen, and no other organic compounds are produced. Therefore, the carbons next to the carbonyl group are the starting points and enols or enolates are formed. A carbonyl compound with an α hydrogen atom is always in equilibrium with its enol. Because of its solubility in THF, LDA is a widely used base for enolate anion formation.

However, in a carbonyl compound, the hydrogen atom of the adjacent carbon atom can be pulled out. This species is known as enolate anion, or enolate for short. That’s because the α-carbon of enolate is negatively charged and has nucleophilic properties as a carbanion. As a result, enolates are synthesized in such a way that many alkyl chains are attached to the double bond. Due to keto-enol tautomerism, both keto and enol forms can change their forms. The LibreTexts libraries are Powered by MindTouch® and are supported by the Department of Education Open Textbook Pilot Project, the UC Davis Office of the Provost, the UC Davis Library, the California State University Affordable Learning Solutions Program, and Merlot. The interconversion between a carbonyl compound and its enol is known as keto-enol tautomerism. Due to these qualities, carbonyl compounds with an α hydrogen can act as an electrophile, as well as a nucleophile, since they possess both an electrophilic carbonyl carbon and a nucleophilic α carbon.

For alkylation reactions of enolate anions to be useful, these intermediates must be generated in high concentration in the absence of other strong nucleophiles and bases. By using a bulky base, a compound can be synthesized to have fewer substituents. Hydroxide functions as a base and removes the acidic α-hydrogen giving the reactive enolate. If the base is present in the solution, it is more likely to react with the alkyl halide. Due to keto-enol tautomerism, the α hydrogen may be easily exchanged for deuterium. There is one problem in the formation of enolates in compounds with electron-withdrawing groups, including ketones. Ether solvents like tetrahydrofuran (THF) are commonly used for enolate anion formation. Organic synthesis using enolates is very convenient because new alkyl chains can be synthesized by the SN2 reaction by adding alkyl halides. If the formed enolate is stabilized by more than one carbonyl it is possible to use a weaker base such as sodium ethoxide.

Enolate, Which Is Nucleophilic and Creates Carbon Bonds in the S, the enolate, as a nucleophilic agent, undergoes the S. Do not add an alkyl halide until after the enolate is formed by the addition of the base. Enolates can be formed from enols using a base.

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