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Chapter 9Ketones and Aldehydes
Carbonyl Compounds
Carbonyl Structure• Carbon is sp2 hybridized.• C=O bond is shorter, stronger, and more
polar than C=C bond in alkenes.
Chapter 9 4
IUPAC Names for Ketones
• Replace -e with -one. Indicate the position of the carbonyl with a number.
• Number the chain so that carbonyl carbon has the lowest number.
• For cyclic ketones the carbonyl carbon is assigned the number 1.
Chapter 9 5
Examples
CH3 C
O
CH
CH3
CH3
O
Br
CH3 C
O
CH
CH3
CH2OH
3-methyl-2-butanone3-methylbutan-2-one 3-bromocyclohexanone
4-hydroxy-3-methyl-2-butanone4-hydroxy-3-methylbutan-2-one
Chapter 9 6
Naming Aldehydes
• IUPAC: Replace -e with -al.• The aldehyde carbon is number 1.• If -CHO is attached to a ring, use the suffix -
carbaldehyde.
Chapter 9 7
Examples
CH3 CH2 CH
CH3
CH2 C H
O
CHO
3-methylpentanal
2-cyclopentenecarbaldehydecyclopent-2-en-1-carbaldehyde
Chapter 9 8
Name as Substituent
• On a molecule with a higher priority functional group, C=O is oxo- and -CHO is formyl.
• Aldehyde priority is higher than ketone.
CH3 C CH
CH3
CH2 C H
OO
COOH
CHO
3-methyl-4-oxopentanal 3-formylbenzoic acid
Chapter 9 9
Common Names for Ketones
• Named as alkyl attachments to -C=O.• Use Greek letters instead of numbers.
CH3 C
O
CH
CH3
CH3 CH3CH C
O
CH
CH3
CH3
Br
methyl isopropyl ketone bromoethyl isopropyl ketone
Chapter 9 10
Historical Common Names
CH3 C
O
CH3
CCH3
O
C
O
acetone acetophenone
benzophenone
Chapter 9 11
Aldehyde Common Names• Use the common name of the acid.• Drop -ic acid and add -aldehyde.
– 1 C: formic acid, formaldehyde– 2 C’s: acetic acid, acetaldehyde– 3 C’s: propionic acid, propionaldehyde– 4 C’s: butyric acid, butyraldehyde.– 5 C’s: valeric acid, valeraldehyde
CH3 CH
Br
CH2 C H
O -bromobutyraldehyde 3-bromobutanal
αβγ
Chapter 9 12
Boiling Points• More polar, so higher boiling point than
comparable alkane or ether.• Cannot H-bond to each other, so lower
boiling point than comparable alcohol.
Chapter 9 13
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.
Chapter 9 14
Formaldehyde
• Gas at room temperature.• Formalin is a 40% aqueous solution.
O
CO
C
OC
H H
H
H
H
H
heatH C
O
HH2O
H CH
OHHO
trioxane, m.p. 62C
formaldehyde,b.p. -21C formalin
Chapter 9 15
Industrial Importance
• Acetone and methyl ethyl ketone are important solvents.
• Formaldehyde used in polymers like Bakelite.
• Flavorings and additives like vanilla, cinnamon, artificial butter.
Chapter 9 16
Synthesis Review
• Oxidation– 2 alcohol + Na2Cr2O7 ketone
– 1 alcohol + PCC aldehyde
• Ozonolysis of alkenes.
Chapter 9 17
Synthesis Review (2)• Friedel-Crafts acylation
– Acid chloride/AlCl3 + benzene ketone
• Hydration of terminal alkyne– Use HgSO4, H2SO4, H2O for methyl ketone
Chapter 9 18
Aldehydes from Acid Chlorides
Use a mild reducing agent to prevent reduction to primary alcohol.
CH3CH2CH2C
O
HLiAlH(O-t-Bu)3CH3CH2CH2C
O
Cl
Chapter 9 19
Ketones from Acid Chlorides
Use lithium dialkylcuprate (R2CuLi), formed by the reaction of 2 moles of R-Li with cuprous iodide.
CH3CH2CH2Li2CuI
(CH3CH2CH2)2CuLi
(CH3CH2CH2)2CuLi + CH3CH2C
O
Cl CH3CH2C
O
CH2CH2CH3
Chapter 18 20
Nucleophilic Addition• A strong nucleophile attacks the
carbonyl carbon, forming an alkoxide ion that is then protonated.
• A weak nucleophile will attack a carbonyl if it has been protonated, thus increasing its reactivity.
• Aldehydes are more reactive than ketones.
Chapter 9 21
Addition of Water• In acid, water is the nucleophile.• In base, hydroxide is the nucleophile.• Aldehydes are more electrophilic since they
have fewer e--donating alkyl groups.
K = 2000C
H H
HOOH
H2O+H
C
O
H
K = 0.002C
CH3 CH3
HOOH
H2O+CH3
C
O
CH3
a gemdiol
a gemdiol
Chapter 9 22
Addition of Alcohol
Chapter 9 23
Mechanism
• Must be acid-catalyzed.• Adding H+ to carbonyl makes it more
reactive with weak nucleophile, ROH.• Hemiacetal forms first, then acid-catalyzed
loss of water, then addition of second molecule of ROH forms acetal.
• All steps are reversible.
Chapter 9 24
Mechanism for Hemiacetal
• Oxygen is protonated.• Alcohol is the nucleophile.• H+ is removed. =>
Chapter 9 25
Hemiacetal to Acetal
+
OCH3HO OCH3
H+
H+
HO OCH3
HOH+
OCH3CH3OOCH3CH3O
H
+
OCH3+
HOCH3
HOCH3
Chapter 18 26
Oxidation of AldehydesEasily oxidized to carboxylic acids.
Chapter 9 27
Cyclic Acetals
• Addition of a diol produces a cyclic acetal.• Sugars commonly exist as acetals or
hemiacetals.
O
CH2 CH2
HO OH+
O OCH2
CH2
Chapter 18 28
Tollens Test
• Add ammonia solution to AgNO3 solution until precipitate dissolves.
• Aldehyde reaction forms a silver mirror.
R C
O
H + 2 + 3 + 2+ 4+Ag(NH3)2+ OH
_ H2O2 Ag R C
O
O_
NH3 H2O
R C
O
H + 2 + 3 + 2+ 4+Ag(NH3)2+ OH
_ H2O2 Ag R C
O
O_
NH3 H2O
=>
SILVER MIRROR
Chapter 18 30
Reduction Reagents
• Sodium borohydride, NaBH4, reduces C=O, but not C=C.
• Lithium aluminum hydride, LiAlH4, much stronger, difficult to handle.
• Hydrogen gas with catalyst also reduces the C=C bond.
Chapter 18 31
Catalytic Hydrogenation
• Widely used in industry.• Raney nickel, finely divided Ni powder
saturated with hydrogen gas.• Pt and Rh also used as catalysts.
ORaney Ni
OH
H
TautormersConstitutional isomers in equilibrium with each other that differ in the location of a hydrogen atom and a double bond are called tautomers.
A case of tautomerization occurs with ketones (aldehydes) that are in equilibrium with their enol form, which are called keto enol tautomers
O OH
Keto Form Enol Form
ALDEHYDE AND KETONE REVIEW
Name
a. Cis-2-pentenalb. Cis-2-pentanalc. Trans-2-pentenald. Trans-2-pentanal
O
CHCH2
CHCH
H3C
Answer
a. Cis-2-pentenalb. Cis-2-pentanalc. Trans-2-pentenald. Trans-2-pentanal
The aldehyde is in position one. The double bond is trans.
Name
a. 2-Oxobutanoic acidb.2-Butanone-1-carbaldehydec. 2-Oxopentanoic acidd.3-Oxopentanoic acid
CH2
C CCH2 OH
OO
H3C
Answer
a. 2-Oxobutanoic acidb.2-Butanone-1-carbaldehydec. 2-Oxopentanoic acidd.3-Oxopentanoic acid
The carbon in the carboxylic acid is position one.
Identify the chemical name for acetone.
a. Methanalb.Ethanalc. Propanoned.Butanone
Answer
a. Methanalb.Ethanalc. Propanoned.Butanone
Acetone is called propanone or dimethyl ketone.
a. 2-Propanoneb.2-Butanonec. 2-Pentanoned.3-Pentanone
1. CH3CH2MgCl
2. H3O+
3. Na2Cr2O7, H2SO4
O
CHH3C
Answer
a. 2-Propanoneb.2-Butanonec. 2-Pentanoned.3-Pentanone
2-Butanone is formed in the Grignard reaction. The secondary alcohol is oxidized to a ketone with sodium dichromate.
a. 2-Propanoneb.2-Butanonec. 2-Pentanoned.3-Pentanone
O
COHH3C
1. CH3CH2Li
2. H3O+
Answer
a. 2-Propanoneb.2-Butanonec. 2-Pentanoned.3-Pentanone
The ethyl group adds to the carbonyl carbon.
a. 2,2-Diethoxypropaneb.2-Ethoxy-2-propanolc. Propane-2,2-diold.2-Ethoxypropane
O
CCH3H3C
2 CH3CH2OH
H+
Answer
a. 2,2-Diethoxypropaneb.2-Ethoxy-2-propanolc. Propane-2,2-diold.2-Ethoxypropane
Two molecules of ethanol are added to the carbonyl, with loss of water.
a. 1-Propanolb.Propanoic acidc. Propane-1,1-diold.1-Hydroxypropanoic acid
O
CHCH2
H3C1. Ag(NH3)2, -OH
2. H+
Answer
a. 1-Propanolb.Propanoic acidc. Propane-1,1-diold.1-Hydroxypropanoic acid
The Tollens reagent reduces an aldehyde to a carboxylic acid.
a. 2-Butanoneb.2-Butanolc. 2-Hexanoned.Butane
O
CCH3CH2
H3CNaBH4
CH3CH2OH
Answer
a. 2-Butanoneb.2-Butanolc. 2-Hexanoned.Butane
Butanone is reduced to 2-butanol.
Chapter 9 50
End of Chapter 9