Condensations and a Substitutions of Carbonyl Compounds

Organic Chemistry Flashcards on Condensations and a Substitutions of Carbonyl Compounds

Alpha Substitution

The substitution of one of the hydrogens attached to the α carbon for an electrophile, occurring through an enolate ion intermediate.

Enolate Ion Condensation

The enolate ion attacks the carbonyl group to form an alkoxide, which, upon protonation, yields a β-hydroxy carbonyl compound.

Condensation with Esters

Enolate addition to an ester to form a tetrahedral intermediate, followed by elimination of alkoxide to yield a β-carbonyl compound.

Tautomerization

An interconversion of isomers through the migration of a proton and the movement of a double bond.

Base-Catalyzed Tautomerism

Abstraction of an α carbon proton to form a resonance-stabilized enolate ion, favoring the keto form at equilibrium.

Acid-Catalyzed Tautomerism

Protonation of oxygen followed by removal of an α carbon proton.

Racemization

Inversion of a chiral α carbon's configuration via an enol intermediate, facilitated by acid or base.

Acidity of α Hydrogens

α Hydrogens of aldehydes or ketones have a pKa of ~20, making them more acidic than alkanes, alkenes, or alkynes, but less acidic than water or alcohols.

Lithium Diisopropylamine (LDA)

A strong, sterically hindered base used to completely convert a carbonyl compound to its enolate.

Alkylation of Enolate Ions

Reaction at the α carbon of an enolate, forming a new C—C bond.

Enamine Formation

Reaction of ketones or aldehydes with a secondary amine, resulting in a nucleophilic α carbon.

Alpha Halogenation of Ketones

The reaction when a ketone is treated with a halogen and a base.

Base-Promoted Halogenation Mechanism

A nucleophilic attack of an enolate ion on the electrophilic halogen molecule, resulting in a halogenated ketone and a halide ion.

Haloform Reaction

The reaction of a methyl ketone with a halogen under strongly basic conditions yielding a carboxylate ion and a haloform molecule.

Iodoform Test

A test used to identify methyl ketones and alcohols that give a positive result, indicated by the precipitation of iodoform (CHI3), a yellow solid.

Acid-Catalyzed α Halogenation

Ketones undergo α halogenation in the presence of an acid catalyst.

Hell-Volhard-Zelinsky (HVZ) Reaction

Replaces a hydrogen atom with a bromine atom on the a carbon of a carboxylic acid (a-bromoacid).

Aldol Condensation

The addition of an enolate ion to another carbonyl group, occurring under basic conditions.

Crossed Aldol Condensations

Occurs when the enolate of one aldehyde (or ketone) adds to the carbonyl group of a different aldehyde or ketone.

Aldol Cyclization

Intramolecular aldol reactions of diketones often used for making five- and six-membered rings.

Claisen Ester Condensation

An ester molecule undergoes nucleophilic acyl substitution by an enolate.

Dieckmann Condensation

An internal Claisen cyclization.

Malonic Ester Synthesis

Makes substituted derivatives of acetic acids through alkylation or acylation of malonic ester.

Acetoacetic Ester Synthesis

Products ketones through a process similar to the malonic ester synthesis.

Michael Reaction

Conjugate addition of a nucleophile to an α,β-unsaturated carbonyl compound.