Alpha-Carbon Chemistry & Carbonyl Condensation Reactions – Chapter 21 Review

Vocabulary flashcards covering alpha-carbon reactivity, halogenation, aldol and Claisen chemistry, enolate alkylation, conjugate additions, and related named reactions from Chapter 21.

α (Alpha) Protons

Hydrogens attached to the carbon directly adjacent (α-carbon) to a carbonyl group.

Enol

Tautomer of a ketone or aldehyde containing a C=C bond and an alcohol; in acid or base it is in equilibrium with the carbonyl form.

Enolate

The anionic species formed when a strong base removes an α-proton from a carbonyl compound; acts as a nucleophile.

Sodium Hydride (NaH)

Strong base that irreversibly converts aldehydes or ketones to enolates under basic conditions.

Lithium Diisopropylamide (LDA)

Non-nucleophilic strong base that completely deprotonates carbonyl α-positions to give enolates irreversibly.

α Halogenation

Substitution of an α-hydrogen of a carbonyl compound by a halogen under acidic or basic conditions.

Autocatalytic α-Halogenation

Acid-catalyzed halogenation that generates HBr, which further catalyzes the reaction itself.

Hell–Volhard–Zelinsky (HVZ) Reaction

α-Halogenation of carboxylic acids using Br₂ and PBr₃ to convert α-hydrogens into α-bromides.

Haloform Reaction

Conversion of a methyl ketone into a carboxylic acid using excess halogen and base, followed by acid work-up.

Aldol Addition

Base-promoted reaction of an enolate with another aldehyde/ketone to yield a β-hydroxy aldehyde or ketone.

β-Hydroxy Carbonyl

Product of an aldol addition containing hydroxyl at the β-position relative to a carbonyl.

Retro-Aldol Reaction

Reverse of aldol addition; favored for most ketones, regenerating the starting carbonyl compounds.

Aldol Condensation

Aldol addition followed by dehydration (E1cb) to give an α,β-unsaturated aldehyde or ketone.

E1cb Mechanism

Elimination pathway involving deprotonation to form an enolate (conjugate base) before loss of a leaving group.

Crossed (Mixed) Aldol Reaction

Aldol reaction between two different carbonyl partners; efficient only when one lacks α-protons or via directed methods.

Intramolecular Aldol Reaction

Aldol reaction within a single molecule that preferentially forms 5- or 6-membered rings.

Claisen Condensation

Reaction of esters with alkoxide base to yield β-keto esters through enolate attack on another ester.

β-Keto Ester

Product containing a ketone at the β-position relative to an ester; hallmark of Claisen condensation.

Crossed Claisen Condensation

Claisen condensation between two different ester partners.

Dieckmann Cyclization

Intramolecular Claisen condensation that forms cyclic β-keto esters.

Enolate Alkylation

Formation of an enolate followed by reaction with an alkyl halide to install an alkyl group at the α-position.

Kinetic Enolate

Enolate formed fastest (less substituted) using LDA at low temperature; alkylation occurs at less hindered α-carbon.

Thermodynamic Enolate

More substituted, more stable enolate obtained with weaker base (e.g., NaH) at higher temperature.

Acetoacetic Ester Synthesis

Method that converts ethyl acetoacetate into substituted acetone derivatives via alkylation and decarboxylation.

Malonic Ester Synthesis

Technique using diethyl malonate to prepare substituted acetic acids after alkylation and decarboxylation.

Decarboxylation of β-Carbonyl Acids

Loss of CO₂ upon heating a carboxylic acid bearing a carbonyl group at the β-position.

Conjugate (1,4) Addition / Michael Reaction

Nucleophilic addition to the β-carbon of an α,β-unsaturated carbonyl compound.

Michael Donor

Nucleophile that adds to the β-position in a Michael reaction.

Michael Acceptor

α,β-Unsaturated carbonyl compound that receives nucleophilic attack in a Michael reaction.

Stork Enamine Synthesis

Formation of an enamine to serve as a Michael donor, enabling conjugate addition to α,β-unsaturated carbonyls.

Robinson Annulation

Sequence of a Michael addition followed by intramolecular aldol condensation to construct cyclic compounds.

1,5-Difunctionalized Compound

Product bearing functional groups at positions 1 and 5; characteristic outcome of Stork enamine synthesis.

1,3-Difunctionalized Compound

Molecule with two functional groups separated by one carbon; produced by aldol additions and Claisen condensations.

α,β Dual Alkylation of Michael Adduct

Treatment of the enolate formed after Michael addition with an alkyl halide to introduce substituents at both α and β positions in a single flask.