Chapter 15
α-Carbon Chemistry: Enols, Enolates, and Enamines
![Reactivity of Enols](https://jovecdn2.ccindex.cn/files/media/science-education/science-education-thumbs/12379.jpg)
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…
![Reactivity of Enolate Ions](https://jovecdn2.ccindex.cn/files/media/science-education/science-education-thumbs/12380.jpg)
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,…
![Enolate Mechanism Conventions](https://jovecdn2.ccindex.cn/files/media/science-education/science-education-thumbs/13054.jpg)
When a carbonyl compound is treated with a strong base, the α position gets deprotonated to give a resonance-stabilized intermediate called an…
![Regioselective Formation of Enolates](https://jovecdn2.ccindex.cn/files/media/science-education/science-education-thumbs/12381.jpg)
As depicted in the figure below, the unsymmetrical ketones can form two possible enolates: less substituted or more substituted enolates.…
![Acid-Catalyzed α-Halogenation of Aldehydes and Ketones](https://jovecdn2.ccindex.cn/files/media/science-education/science-education-thumbs/12382.jpg)
By replacing an α-hydrogen with a halogen, acid-catalyzed α-halogenation of aldehydes or ketones yields a monohalogenated product
In the…
![Base-Promoted α-Halogenation of Aldehydes and Ketones](https://jovecdn2.ccindex.cn/files/media/science-education/science-education-thumbs/12383.jpg)
α-Halogenation of aldehydes and ketones is a reaction involving the substitution of α hydrogens with halogens in the presence of a…
![α-Halogenation of Carboxylic Acid Derivatives: Overview](https://jovecdn2.ccindex.cn/files/media/science-education/science-education-thumbs/11931.jpg)
Unlike aldehydes and ketones, carboxylic acids do not readily participate in α halogenation reactions via enols or enolate intermediates.…
![α-Bromination of Carboxylic Acids: Hell–Volhard–Zelinski Reaction](https://jovecdn2.ccindex.cn/files/media/science-education/science-education-thumbs/12384.jpg)
The method to achieve α-brominated carboxylic acids using a mixture of phosphorus tribromide and bromine is known as the…
![Nitrosation of Enols](https://jovecdn2.ccindex.cn/files/media/science-education/science-education-thumbs/13215.jpg)
The nitrosation reaction is one of the methods of preparing 1,2-diketones. The enol tautomer of the starting ketone reacts with sodium nitrite in…
![C–C Bond Formation: Aldol Condensation Overview](https://jovecdn2.ccindex.cn/files/media/science-education/science-education-thumbs/13061.jpg)
Aldol condensation is an important route in synthetic organic chemistry used to generate a new carbon–carbon bond under basic or acidic…
![Acid-Catalyzed Aldol Addition Reaction](https://jovecdn2.ccindex.cn/files/media/science-education/science-education-thumbs/13062.jpg)
The aldol reaction of a ketone under acidic conditions successfully forms an unsaturated carbonyl as the final product instead of an aldol. The…
![Dehydration of Aldols to Enals: Base-Catalyzed Aldol Condensation](https://jovecdn2.ccindex.cn/files/media/science-education/science-education-thumbs/12386.jpg)
This lesson delves into the aldol condensation catalyzed by bases, where aldols undergo dehydration to enals. As shown in Figure 1, the…
![Intramolecular Aldol Reaction](https://jovecdn2.ccindex.cn/files/media/science-education/science-education-thumbs/12387.jpg)
Intramolecular aldol reaction occurs in dicarbonyl compounds such as dialdehydes, diketones, and keto-aldehydes. The dicarbonyl compounds possess…
![C–C Bond Cleavage: Retro-Aldol Reaction](https://jovecdn2.ccindex.cn/files/media/science-education/science-education-thumbs/13064.jpg)
The reverse of the aldol addition reaction is called the retro-aldol reaction. Here, the carbon–carbon bond in the aldol product is cleaved…
![Crossed Aldol Reaction Using Weak Bases](https://jovecdn2.ccindex.cn/files/media/science-education/science-education-thumbs/12388.jpg)
This lesson deals with the crossed aldol reaction using weak bases. The self-condensation of an aldehyde having α hydrogen is prevented by…
![Ketones with Nonenolizable Aromatic Aldehydes: Claisen–Schmidt Condensation](https://jovecdn2.ccindex.cn/files/media/science-education/science-education-thumbs/13066.jpg)
Benzaldehyde, like formaldehyde, lacks an α hydrogen and cannot enolize to form an enolate. Hence, the reaction of benzaldehyde with a ketone in…
![Aldol Condensation with β-Diesters: Knoevenagel Condensation](https://jovecdn2.ccindex.cn/files/media/science-education/science-education-thumbs/13068.jpg)
The Knoevenagel condensation is an aldol-type reaction involving the condensation of aldehydes or ketones with active methylene compounds such as…
![Esters to β-Ketoesters: Claisen Condensation Overview](https://jovecdn2.ccindex.cn/files/media/science-education/science-education-thumbs/12390.jpg)
Regular Claisen condensation is a base-promoted reaction involving identical esters with two α hydrogens, condensing to produce…
![Aldol Condensation vs Claisen Condensation](https://jovecdn2.ccindex.cn/files/media/science-education/science-education-thumbs/13070.jpg)
Aldol condensation is an acid or base-catalyzed condensation between aldehydes or ketones to give an α,ꞵ-unsaturated carbonyl…
![Intramolecular Claisen Condensation of Dicarboxylic Esters: Dieckmann Cyclization](https://jovecdn2.ccindex.cn/files/media/science-education/science-education-thumbs/12391.jpg)
Dieckmann cyclization is an intramolecular Claisen condensation of diesters. The reaction occurs in the presence of a base and generates a cyclic…
![α-Alkylation of Ketones via Enolate Ions](https://jovecdn2.ccindex.cn/files/media/science-education/science-education-thumbs/12393.jpg)
Ketones with α protons are deprotonated by strong bases like lithium diisopropylamide (LDA) to form enolate ions. The anion is stabilized by…
![Factors Affecting α-Alkylation of Ketones: Choice of Base](https://jovecdn2.ccindex.cn/files/media/science-education/science-education-thumbs/13072.jpg)
α-Alkylation of ketones is achieved in the presence of alkyl halides and a base. The reaction proceeds via the formation of an enolate ion…
![Alkylation of β-Diester Enolates: Malonic Ester Synthesis](https://jovecdn2.ccindex.cn/files/media/science-education/science-education-thumbs/13075.jpg)
Malonic ester synthesis is a method to obtain α substituted carboxylic acids from ꞵ-diesters such as diethyl malonate and alkyl…
![Conjugate Addition to α,β-Unsaturated Carbonyl Compounds](https://jovecdn2.ccindex.cn/files/media/science-education/science-education-thumbs/12396.jpg)
α,β-Unsaturated carbonyl compounds are molecules bearing a carbonyl and alkene functionality in conjugation with each other. The…
![Conjugate Addition of Enolates: Michael Addition](https://jovecdn2.ccindex.cn/files/media/science-education/science-education-thumbs/12397.jpg)
The attack of a nucleophile at the β carbon of an α,β-unsaturated carbonyl compound is called conjugate addition. Conjugate addition…
![Cyclohexenones via Michael Addition and Aldol Condensation: The Robinson Annulation](https://jovecdn2.ccindex.cn/files/media/science-education/science-education-thumbs/13079.jpg)
Robinson annulation is a base-catalyzed reaction for the synthesis of 2-cyclohexenone derivatives from 1,3-dicarbonyl donors (such as cyclic…
![Synthesis of Indoxyl-glycosides for Detection of Glycosidase Activities](https://jovecdn2.ccindex.cn/files/thumbs/52442_t.png)
Indoxyl glycosides proved to be valuable and versatile tools for monitoring glycosidase activities. Indoxyls are released by enzymatic hydrolysis and…
![Designed for Molecular Recycling: A Lignin-Derived Semi-aromatic Biobased Polymer](https://jovecdn2.ccindex.cn/files/thumbs/61975_t.png)
The development of chemically recyclable biopolymers offers opportunities within the pursuit of a circular economy. Chemically recyclable biopolymers…