Untitled Quiz

Ketones and Aldehydes

• Ketones and aldehydes are carbonyl compounds

• Carbonyl structure: Carbon is sp² hybridized. C=O bond is shorter and stronger, more polar than C=C bond in alkenes.

• Ketone C=O bond length: 1.23 Å

• Ketone C=O bond energy: 178 kcal/mol (745 kJ/mol)

• Alkene C=C bond length: 1.34 Å

• Alkene C=C bond energy: 146 kcal/mol (611 kJ/mol)

Naming Aldehydes

• IUPAC: Replace -e with -al.
• The aldehyde carbon is number 1.
• If -CHO is attached to a ring, use the suffix -carbaldehyde.

Examples

• 3-methylpentanal
• 2-cyclopentenecarbaldehyde

Aldehydes: Common Names

• Formaldehyde (Methanal)
• Acetaldehyde (Ethanal)
• Propionaldehyde (Propanal)
• Butyraldehyde (Butanal)
• 2-Chloropropanal
• 3-Hydroxypropanal
• Benzaldehyde
• p-Nitrobenzaldehyde
• o-Hydroxybenzaldehyde
• p-Methoxybenzaldehyde
• Salicylaldehyde
• Anisaldehyd

IUPAC Names for Ketones

• Replace -e with -one.
• Indicate the position of the carbonyl with a number.
• Number the chain so that the carbonyl carbon has the lowest number.
• For cyclic ketones, the carbonyl carbon is assigned the number 1.

Examples

• 3-methyl-2-butanone
• 3-bromocyclohexanone
• 4-hydroxy-3-methyl-2-butanone

Naming as Substituent

• On a molecule with higher priority functional group, C=O is oxo- and -CHO is formyl.
• Aldehyde priority is higher than ketone.

Common Names for Ketones

• Named as alkyl attachments to -C=O.
• Use Greek letters instead of numbers.

Examples

• Methyl isopropyl ketone
• α-bromoethyl isopropyl ketone

Historical Common Names

• Acetone
• Acetophenone
• Benzophenone

Boiling Points

• More polar, has higher boiling point than comparable alkane or ether.
• Cannot form H-bonds with each other, so has lower boiling point than comparable alcohols.

Solubility

• Good solvent for alcohols.
• Lone pair of electrons on oxygen of carbonyl can accept a hydrogen bond from O-H or N-H.
• Acetone and acetaldehyde are miscible in water.

Industrial Importance

• Acetone and methyl ethyl ketone are important solvents.
• Formaldehyde is used in polymers like Bakelite.
• Flavorings and additives like vanilla, cinnamon, and artificial butter.

Preparation of Aldehydes and Ketones

• Oxidation of alcohols
• Reduction of acid chlorides
• Ozonolysis of alkenes
• Hydration of alkynes (Kocherov's reaction) -Hydroboration-oxidation
• Friedel-Crafts acylation
• Hydroformylation reaction
• Gattermann-Koch reaction
• Reimer-Tiemann reaction
• Oxidation of an alkyl side of aromatic ring.
• From acid chloride and lithium dialkyl cuperate or R₂Cd
• From nitriles and Grignard reagent or alkyl lithium
• From carboxylates

Knoevenagel

• Condensation of active methylene compounds with aldehydes
• To give a, β-unsaturated compounds

Stobbe Condensation

• Modification for diethyl ester of succinic acid

Benzoin Condensation

• Condensation of aldehydes devoid of α-hydrogen
• Preparation of α-hydroxyketones

Wittig Reaction

• Nucleophilic addition of phosphorous ylides
• Product is alkene (C=C)

Phosphorus Ylides

• Prepared from triphenylphosphine and unhindered alkyl halide.
• Butyllithium abstracts a hydrogen from the carbon attached to phosphorous

Mechanism of Wittig Reaction

• The negative C on ylide attacks the positive C of carbonyl to form a betaine.
• Oxygen combines with phosphorous to form phosphorous oxide.

Oxidation of Aldehyde

• Easily oxidized to carboxylic acids

Tollens Test

• Add ammonia solution to AgNO3 solution until precipitate dissolves.
• Aldehyde reaction forms a silver mirror.

Iodoform Reaction

• Oxidation of a methyl ketone to a carboxylate.
• Alpha position to carbonyl easily halogenated.

Cannizzaro Reaction

• Redox disproportionation of non-enolizable aldehydes.
• Gives carboxylic acids and alcohols.

Aldol Reactions

• Condensation reaction of two carbonyl compounds.

Intramolecular Aldol Condensation

• Even ketones give good yields when reaction is intramolecular.

Aromatic Aldehydes

• Reaction of aldehydes with reactive methyl group.

Perkin Reaction

• α,β-unsaturated aromatic acid by aldol type condensation.
• Aromatic aldehydes, acid anhydride with an alkali salt.

Claisen Condensation

• Base-promoted condensation of two esters.
• To give β-keto-ester product.

Crossed Claisen Condensations

• Similar restrictions as mixed aldol condensation.

Dieckmann Cyclization

• Intramolecular Claisen Condensation.

Acylation of Ketones with Esters

• Alternative to Claisen condensations.
• Dieckmann cyclization.

Meerwein-Ponndorf-Verley reduction

• Reduction of carbonyl to alcohols using aluminum alkoxide catalysts.
• Chemoselective (aldehydes reduced before ketones).

Oppenauer oxidation

• Oxidation of secondary alcohols to ketones.
• Opposite to MPV reduction.

Deoxygenation

• Reduction of C=O to CH2
• Two methods:
  • Clemmensen reduction (stable in acid)
  • Wolff-Kishner reduction (stable in strong base)

Clemmensen Reduction

• Deoxygenation of aldehydes or ketones to hydrocarbons.

Wolff-Kishner Reduction

• Deoxygenation using hydrazine and a strong base.

Huang Minlon Modification

• Modification to the Wolff-Kishner reduction.
• Refluxing the carbonyl substrate with hydrazine hydrate and sodium hydroxide in ethylene glycol.