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Chapter 9Ketones and Aldehydes
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Carbonyl Compounds
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Carbonyl Structure• Carbon is sp2 hybridized.• C=O bond is shorter, stronger, and more
polar than C=C bond in alkenes.
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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.
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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
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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.
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Chapter 9 7
Examples
CH3 CH2 CH
CH3
CH2 C H
O
CHO
3-methylpentanal
2-cyclopentenecarbaldehydecyclopent-2-en-1-carbaldehyde
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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
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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
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Chapter 9 10
Historical Common Names
CH3 C
O
CH3
CCH3
O
C
O
acetone acetophenone
benzophenone
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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
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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.
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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.
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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
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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.
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Chapter 9 16
Synthesis Review
• Oxidation– 2 alcohol + Na2Cr2O7 ketone
– 1 alcohol + PCC aldehyde
• Ozonolysis of alkenes.
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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
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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
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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
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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.
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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
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Chapter 9 22
Addition of Alcohol
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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.
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Chapter 9 24
Mechanism for Hemiacetal
• Oxygen is protonated.• Alcohol is the nucleophile.• H+ is removed. =>
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Chapter 9 25
Hemiacetal to Acetal
+
OCH3HO OCH3
H+
H+
HO OCH3
HOH+
OCH3CH3OOCH3CH3O
H
+
OCH3+
HOCH3
HOCH3
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Chapter 18 26
Oxidation of AldehydesEasily oxidized to carboxylic acids.
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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
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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
=>
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SILVER MIRROR
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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.
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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
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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
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ALDEHYDE AND KETONE REVIEW
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Name
a. Cis-2-pentenalb. Cis-2-pentanalc. Trans-2-pentenald. Trans-2-pentanal
O
CHCH2
CHCH
H3C
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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.
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Name
a. 2-Oxobutanoic acidb.2-Butanone-1-carbaldehydec. 2-Oxopentanoic acidd.3-Oxopentanoic acid
CH2
C CCH2 OH
OO
H3C
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Answer
a. 2-Oxobutanoic acidb.2-Butanone-1-carbaldehydec. 2-Oxopentanoic acidd.3-Oxopentanoic acid
The carbon in the carboxylic acid is position one.
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Identify the chemical name for acetone.
a. Methanalb.Ethanalc. Propanoned.Butanone
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Answer
a. Methanalb.Ethanalc. Propanoned.Butanone
Acetone is called propanone or dimethyl ketone.
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a. 2-Propanoneb.2-Butanonec. 2-Pentanoned.3-Pentanone
1. CH3CH2MgCl
2. H3O+
3. Na2Cr2O7, H2SO4
O
CHH3C
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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.
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a. 2-Propanoneb.2-Butanonec. 2-Pentanoned.3-Pentanone
O
COHH3C
1. CH3CH2Li
2. H3O+
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Answer
a. 2-Propanoneb.2-Butanonec. 2-Pentanoned.3-Pentanone
The ethyl group adds to the carbonyl carbon.
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a. 2,2-Diethoxypropaneb.2-Ethoxy-2-propanolc. Propane-2,2-diold.2-Ethoxypropane
O
CCH3H3C
2 CH3CH2OH
H+
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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.
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a. 1-Propanolb.Propanoic acidc. Propane-1,1-diold.1-Hydroxypropanoic acid
O
CHCH2
H3C1. Ag(NH3)2, -OH
2. H+
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Answer
a. 1-Propanolb.Propanoic acidc. Propane-1,1-diold.1-Hydroxypropanoic acid
The Tollens reagent reduces an aldehyde to a carboxylic acid.
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a. 2-Butanoneb.2-Butanolc. 2-Hexanoned.Butane
O
CCH3CH2
H3CNaBH4
CH3CH2OH
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Answer
a. 2-Butanoneb.2-Butanolc. 2-Hexanoned.Butane
Butanone is reduced to 2-butanol.
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Chapter 9 50
End of Chapter 9