Organic Chemistry - Substitution Reactions of Carbonyl Compounds at the α-Carbon

These flashcards cover key concepts from organic chemistry focusing specifically on the substitution reactions of carbonyl compounds.

What types of reactions can carbonyl compounds undergo at the carbon that is α to the carbonyl group?

Substitution of an electrophile E+ for hydrogen.

What are keto-enol tautomers?

Constitutional isomers of the carbonyl group that differ in the position of a double bond and a proton.

In most carbonyl compounds, which form, keto or enol, is favored at equilibrium?

The keto form is favored because the C=O bond is much stronger than a C=C bond.

In β-dicarbonyl compounds, which form can sometimes exceed in concentration?

The enol form can sometimes exceed the concentration of the keto form due to conjugation and intramolecular hydrogen bonding.

How is tautomerization catalyzed in acids?

Protonation of the carbonyl forms a resonance-stabilized carbocation, followed by deprotonation to form the enol.

What is the effect of the OH group on the reactivity of enols?

The OH group makes enols more electron-rich and thus more reactive toward electrophiles.

What comparative acidity is observed in the C—H bonds of α carbons?

The C—H bond on the α carbon is more acidic (pKa ~20) than most sp3 hybridized C—H bonds.

How do enolates react with electrophiles?

Enolates react with electrophiles at the α carbon.

What occurs during the halogenation of a ketone or aldehyde with halogen and acid or base?

Substitution of X for H on the α carbon, forming an α-halo ketone or aldehyde.

What is the Haloform reaction?

A reaction where three hydrogen atoms in a CH3 group are replaced by halogens, yielding iodoform from methyl ketones.

What is the main difference between the acetoacetic ester synthesis and the malonic ester synthesis?

Acetoacetic ester synthesis produces ketones, whereas malonic ester synthesis produces carboxylic acids.

What type of base is Lithium diisopropylamide (LDA)?

A strong nonnucleophilic base that can form an enolate in essentially 100% yield.