Ch. 6 - Aldehydes and Ketones I: Electrophilicity and Oxidation— Reduction

8% of MCAT Organic content

What are aldehydes, and how are they named?

• Terminal functional groups with a carbonyl bonded to at least one hydrogen.

• Suffix: -al

• Prefix: oxo-

• In rings: -carbaldehyde.

What are ketones, and how are they named?

• Internal functional groups with a carbonyl bonded to two alkyl chains.

• Suffix: -one

• Prefix: oxo- or keto-.

What dictates the reactivity of the carbonyl group?

Polarity of the C=O bond:

Carbon is electrophilic due to a partial positive charge.

How do boiling points compare among alkanes, carbonyls, and alcohols?

Alcohols (hydrogen bonding) > Carbonyls (dipole interactions) > alkanes

How are aldehydes and ketones commonly produced?

• Aldehydes: Oxidation of primary alcohols (using weaker, anhydrous agents like PCC).

• Ketones: Oxidation of secondary alcohols (using PCC, dichromate, or CrO₃).

What happens in nucleophilic addition reactions with carbonyls?

1. Nucleophile attacks carbonyl carbon, and π electrons shift to oxygen.

2. Without a leaving group (aldehydes/ketones): Forms an alcohol after protonation.

3. With a leaving group (carboxylic acids/derivatives): Forms a carbonyl after kicking off the leaving group.

What is formed during hydration reactions of carbonyls?

Water reacts to form a geminal diol.

What is formed when alcohol reacts with aldehydes and ketones?

1 equivalent of alcohol

• Aldehyde → Hemiacetal

• Ketone → Hemiketal

2 equivalents of alcohol

• Hemiacetal → Acetal

• Hemiketal → Ketal

What reactions occur between nitrogen compounds and carbonyls?

• Form imines, oximes, hydrazones, and semicarbazones.

• Imines can tautomerize to form enamines.

How does hydrogen cyanide react with carbonyls?

Forms cyanohydrins.

How can aldehydes be oxidized and reduced?

• Oxidized to carboxylic acids using KMnO₄, CrO₃, Ag₂O, or H₂O₂.

• Reduced to primary alcohols using hydride reagents (LiAlH₄, NaBH₄).

How can ketones be reduced?

• Reduced to secondary alcohols using hydride reagents (LiAlH₄, NaBH₄).

• Cannot be further oxidized.