Classes of Carbonyl Compounds

Carbonyl
• C=O bond is shorter, stronger and more polar than C=C bond in alkenes

Nomenclature: Ketone
• Number chain so the carbonyl carbon has the lowest number
• Replace “e” with “one”

Nomenclature: Cyclic Ketone
• Carbonyl carbon is #1

Nomenclature: Aldehydes
• Carbonyl carbon is #1
• Replace “e” with “al”
• If aldehyde is attached to ring, suffix
“carbaldehyde” is used

Nomenclature
• With higher-priority functional groups, ketone is
“oxo” and an aldehyde is a “formyl” group
• Aldehydes have higher priority than ketones

Nomenclature- Common Names: Ketones
• Name alkyl groups attached to carbonyl
• Use lower case Greek letters instead of numbers

Nomenclature

Boiling Points
• Ketones and aldehydes are more polar. Have higher boiling point that comparable alkanes or ethers

Solubility: Ketones and Aldehydes
• Good solvent for alcohols
• Acetone and acetaldehyde are miscible in water

Formaldehyde
• Gas at room temperature

IR Spectroscopy
• Strong C=O stretch around 1710 cm -1 (ketones) or 1725 cm -1 (simple aldehydes)
• C-H stretches for aldehydes: 2710 and 2810 cm -1

IR Spectroscopy
• Conjugation lowers carbonyl frequencies to about 1685 cm -1
• Rings with ring strain have higher C=O frequencies

Proton NMR Spectra
• Aldehyde protons normally around δ9-10
• Alpha carbon around δ2.1-2.4

Carbon NMR Spectra

Mass Spectrometry (MS)

Mass Spectrometry (MS)

Mass Spectrometry (MS)

McLafferty Rearrangement
• Net result: breaking of the
,  bond and transfer of a proton from the
 carbon to oxygen

Ultraviolet Spectra of Conjugated Carbonyls
• Have characteristic absorption in UV spectrum
• Additional conjugate C=C increases
 max about
30 nm, additional alkyl groups increase about
10nm

Carbonyl Electronic Transitions

Industrial Uses
• Acetone and methyl ethyl ketone are common solvents
• Formaldehyde is used in polymers like Bakelite and other polymeric products

• Used as flavorings and additives for food

Industrial Uses

Synthesis of Aldehydes and Ketones
• The alcohol product of a Grignard reaction can be oxidized to a carbonyl

Synthesis of Aldehydes and Ketones
• Pyridinium chlorochromate (PCC) or a Swern oxidation takes primary alcohols to aldehydes

Synthesis of Aldehydes and Ketones
• Alkenes can be oxidatively cleaved by ozone, followed by reduction

Synthesis of Aldehydes and Ketones
• Friedel-Crafts Acylation

Synthesis of Aldehydes and Ketones
• Hydration of Alkynes
• Involves a keto-enol tautomerization
• Mixture of ketones seen with internal alkynes

Synthesis of Aldehydes and Ketones
• Hydroboration-oxidation of alkyne
• Anti-Markovnikov addition

Synthesis Problem

Synthesis of Aldehydes and Ketones
• Organolithium + carboxylic acid  ketone (after dehydration)

Synthesis of Aldehydes and Ketones
• Grignard or organolithium reagent + nitrile  ketone (after hydrolysis)

Synthesis of Aldehydes and Ketones
• Reduction of nitriles with aluminum hydrides will afford aldehydes

Synthesis of Aldehydes and Ketones
• Mild reducing agent lithium aluminum tri(tbutoxy)hydride with acid chlorides

Synthesis of Aldehydes and Ketones
• Organocuprate (Gilman reagent) + acid chloride  ketone

Nucleophilic Addition
• Aldehydes are more reactive than ketones

Wittig Reaction
• Converts the carbonyl group into a new C=C bond
• Phosphorus ylide is used as the nucleophile

Wittig Reaction
• Phosphorus ylides are prepared from triphenylphosphine and an unhindered alkyl halide
• Butyllithium then abstracts a hydrogen from the carbon attached to phosphorus

Wittig Reaction- Mechanism
• Betaine formation
• Oxaphosphetane formation

Wittig Reaction- Mechanism
• Oxaphosphetane collapse

How would you synthesize the following molecule using a Wittig Reaction

Hydration of Ketones and Aldehydes
• In aqueous solution, a ketone or aldehyde is in equilibrium with it’s hydrate
• Ketones: equilibrium favors keto form

Hydration of Ketones and Aldehydes
• Acid-Catalyzed

Hydration of Ketones and Aldehydes
• Base-Catalyzed

Cyanohydrin Formation
• Base-catalyzed nucleophilic addition
• HCN is highly toxic

Formation of Imines
• Imines are nitrogen analogues of ketones and aldehydes
• Optimum pH is around 4.5

Formation of Imines- Mechanism

Condensations with Amines

Acetal Formation

Hemiacetal Formation- Mechanism
• Must be acid-catalyzed

Acetal Formation- Mechanism
• Must be acid-catalyzed

Hydrolysis of Acetals
• Acetals can be hydrolyzed by addition of dilute acid
• Excess of water drives equilibrium towards carbonyl formation

Cyclic Acetals
• Addition of diol produces cyclic acetal
• Reaction is reversible
• Used as a protecting group
• Stable in base, hydrolyze in acid

Cyclic Acetals- Protecting Group
O
O
O
H
1) NaBH
4
2) H
3
O
+
OH
O
H
• Acetals are stable in base, only ketone reduces
• Hydrolysis conditions protonate the alkoxide and restore the aldehyde

Oxidation of Aldehydes
• Easily oxidized to carboxylic acids

Tollens Test
• Involves a solution of silver-ammonia complex to the unknown compound
• If an aldehyde is present, its oxidation reduces silver ion to metallic silver

Reducing Reagents- Sodium Borohydride
• NaBH
4 can reduce ketones and aldehydes, not esters, carboxylic acids, acyl chlorides, or amides

Reducing Reagents- Lithium Aluminum Hydride
• LiAlH
4 can reduce any carbonyl
O
R R(H) aldehyde or ketone
LiAlH
4 ether
OH
R
H
R(H)

Reducing Reagents- Catalytic Hydrogenation
• Widely used in industry
• Raney nickel is finely divided Ni powder saturated with hydrogen gas
• Will attack alkene first, then carbonyl

Deoxygenation of Ketones and Aldehydes
• Clemmensen reduction or Wolff-Kishner reactions can deoxygenate ketones and aldehydes

Clemmensen Reduction
• Uses Zinc-Mercury amalgam in aqueous HCl

Wolff-Kishner Reduction
• Forms hydrazone, then needs heat with strong base like KOH or potassium tert-butoxide
• Use high-boiling solvent (ethylene glycol, diethylene glycol, or DMSO)