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Reactivity of Enolate Ions

Reactivity of Enolate Ions

Enolate ions are formed by the acid–base reaction of a carbonyl compound with a base. This leads to deprotonation of the α hydrogen atom, leading to a resonance-stabilized enolate ion where one of the contributing structures is an oxyanion, which imparts additional stability. Therefore, the proton on the α carbon is more acidic in nature than that of other sp3-hybridized C–H bonds but less acidic than those in O–H bonds where the negative charge in the conjugate...

Enolate Mechanism Conventions

Enolate Mechanism Conventions

When a carbonyl compound is treated with a strong base, the α position gets deprotonated to give a resonance-stabilized intermediate called an enolate. Enolates are ambident nucleophiles because they possess two nucleophilic sites that can attack an electrophile owing to the delocalization of the negative charge between the α carbon and oxygen atoms. When the oxygen atom attacks an electrophile, it is called O-attack, whereas electrophilic attack via the α carbon is known as...

α-Alkylation of Ketones via Enolate Ions

α-Alkylation of Ketones via Enolate Ions

Ketones with α protons are deprotonated by strong bases like lithium diisopropylamide (LDA) to form enolate ions. The anion is stabilized by resonance, and its hybrid structure exhibits negative charges on the carbonyl oxygen and the α carbon. This ambident nucleophile can attack an electrophile via two possible sites: the carbonyl oxygen, known as O-attack, or the α carbon, known as C-attack. The nucleophilic attack via the carbanionic site is preferred. This is due to the...

Regioselective Formation of Enolates

Regioselective Formation of Enolates

As depicted in the figure below, the unsymmetrical ketones can form two possible enolates: less substituted or more substituted enolates. Usually, the thermodynamic enolates are formed from the more substituted α-carbon atom, while the kinetic enolates are formed faster by deprotonation from the less substituted position. The thermodynamic enolates have lower energy, so they are more stable. But the energy required to form kinetic enolates is less.

Reactivity of Enols

Reactivity of Enols

Enols are a class of compounds where a hydroxyl group is attached to a carbon–carbon double bond, which implies that it is a vinyl alcohol. A carbonyl compound with an α hydrogen undergoes keto–enol tautomerism and remains in equilibrium with its tautomer, the enol form. Usually, the keto tautomer is present in a higher concentration than the enol tautomer due to the higher bond energy of C=O compared to C=C. Moreover, the direction of the keto–enol equilibrium is...

Electrophiles

Electrophiles

This lesson explains the definition, classification, and characteristic features of an electrophile that are key features of nucleophilic substitution reactions. An analysis of their charge and orbital picture helps understand their reactivity for seeking electrons. Electrophiles can be classified into positive and neutral species. Other classes include free radicals and polar functional groups.
While a positive electrophile, like a proton, reacts due to its vacant, low-energy 1s orbital, the...

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Related Experiment Video

Updated: Apr 29, 2026

A Two-Step Protocol for Umpolung Functionalization of Ketones Via Enolonium Species

A Two-Step Protocol for Umpolung Functionalization of Ketones Via Enolonium Species

Published on: August 16, 2018

Enolate chemistry with anion-π interactions.

Yingjie Zhao¹, Naomi Sakai¹, Stefan Matile¹

¹Department of Organic Chemistry, University of Geneva, Geneva CH-1211, Switzerland.

Nature Communications

|May 22, 2014

Summary

This summary is machine-generated.

Anion-π interactions can stabilize reactive enolates, enhancing their addition to other molecules. This discovery opens new avenues for catalysis in chemistry and biology.

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A Protocol for Safe Lithiation Reactions Using Organolithium Reagents

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Facile Preparation of 2Z,4E-Dienamides by the Olefination of Electron-deficient Alkenes with Allyl Acetate

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Published on: June 21, 2017

Area of Science:

Supramolecular Chemistry
Organic Chemistry
Catalysis

Background:

Anion-π interactions involve π-acidic aromatic systems and are known for anion binding and transport.
Their role in stabilizing reactive intermediates and transition states is largely unexplored, unlike cation-π interactions crucial in biological catalysis.

Purpose of the Study:

To investigate the potential of anion-π interactions in stabilizing anionic reactive intermediates and transition states.
To explore the impact of anion-π interactions on the reactivity of enolates.

Main Methods:

Experimental evidence was gathered to demonstrate the stabilizing effect of anion-π interactions.
The stabilization of enolates and subsequent reactions were quantified.

Main Results:

Single, unoptimized anion-π interactions were shown to stabilize enolates by approximately two pKa units.
Transition-state stabilization of up to 11 kJ mol⁻¹ was observed for the addition of stabilized enolates to enones and nitroolefins.
Anionic cascade reactions were accelerated on π-acidic surfaces.

Conclusions:

Anion-π interactions significantly stabilize reactive enolate intermediates.
These interactions provide substantial transition-state stabilization, accelerating key chemical reactions.
The findings highlight the potential of anion-π interactions for broad applications in catalysis, particularly in enolate chemistry central to biology and chemistry.