Chapter 9
Ketones 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.
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
4
Examples
O
O
CH3
C CH CH3
CH3
Br
3-methyl-2-butanone
3-methylbutan-2-one
3-bromocyclohexanone
O
CH3
C CH CH2OH
CH3
4-hydroxy-3-methyl-2-butanone
4-hydroxy-3-methylbutan-2-one
Chapter 9
5
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
6
Examples
CH3
CH2
CH3
O
CH CH2
C H
3-methylpentanal
CHO
2-cyclopentenecarbaldehyde
cyclopent-2-en-1-carbaldehyde
Chapter 9
7
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.
COOH
CH3
O
CH3
O
C
CH CH2
C H
CHO
3-methyl-4-oxopentanal
3-formylbenzoic acid
Chapter 9
8
Common Names for Ketones
• Named as alkyl attachments to -C=O.
• Use Greek letters instead of numbers.
O
O
CH3
CH3CH C CH CH3
C CH CH3
Br
CH3
methyl isopropyl ketone
CH3
a-bromoethyl isopropyl ketone
Chapter 9
9
Historical Common Names
O
C
O
CH3
CH3
C CH3
acetophenone
acetone
O
C
benzophenone
Chapter 9
10
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
Br
CH3
γ
O
CH CH2
β
α
C H
-bromobutyraldehyde
3-bromobutanal
Chapter 9
11
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
12
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
13
Formaldehyde
• Gas at room temperature.
• Formalin is a 40% aqueous solution.
H
H
H
O
C
H
C
O
O
C H
O
H
heat
H C H
formaldehyde,
b.p. -21C
H2O
HO
OH
H C
H
formalin
trioxane, m.p. 62C
Chapter 9
14
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
15
Synthesis Review
• Oxidation
– 2 alcohol + Na2Cr2O7  ketone
– 1 alcohol + PCC  aldehyde
• Ozonolysis of alkenes.
Chapter 9
16
Synthesis Review (2)
• Friedel-Crafts acylation
– Acid chloride/AlCl3 + benzene  ketone
• Hydration of terminal alkyne
– Use HgSO4, H2SO4, H2O for methyl ketone
Chapter 9
17
Aldehydes from Acid Chlorides
Use a mild reducing agent to prevent
reduction to primary alcohol.
O
CH3CH2CH2C
O
Cl
LiAlH(O-t-Bu)3
Chapter 9
CH3CH2CH2C
H
18
Ketones from Acid Chlorides
Use lithium dialkylcuprate (R2CuLi), formed by
the reaction of 2 moles of
R-Li with cuprous iodide.
2 CH3CH2CH2- Li+
(CH3CH2)22-CuLi2+ + LiI
+ CuI
O
(CH3CH2CH2)2CuLi +
O
CH3CH2C Cl
Chapter 9
CH3CH2C CH2CH2CH3
19
CARBONYL REACTIONS
When adding electrophiles or nucleophiles, the stronger one adds
first. In electrophilic addition the result is the oxonium ion which is
stabilized by resonance giving a carbocation, which in turn is
neutralized by an electrophile. In nucleophilic addition the result is
the enolate ion and the negatively charged oxygen is quenched by
an electrophile. The resultant product is the electrophile bonded to
oxygen and the nucleophile bonded to the carbonyl carbon.
Electrophiles and Nucleophiles
An electrophile is an electron poor species, lacking a
nobel configuration. A strong electrophile would contain
a positive charge, i.e. a proton from an acid.
Nucleophiles are electron rich substances with at least
on nonbonding pair of electrons. Strong nucleophiles
would have a negative charge.
Nucleophiles
HOH
ROH
NH3
HRRO-
Electrophiles
H+
FeCl3
AlCl3
BH3
CARBONYL REACTIONS
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 18
22
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.
O
H
HO
+ H2O
C
H
OH
C
H
H
K = 2000
a gemdiol
O
CH3
C
HO
+ H2O
CH3
CH3
OH
C
CH3
K = 0.002
a gemdiol
Chapter 9
23
Addition of Alcohol
Chapter 9
24
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
25
Mechanism for Hemiacetal
• Oxygen is protonated.
• Alcohol is the nucleophile.
• H+ is removed.
Chapter 9
=>
26
Hemiacetal to Acetal
HO
OCH3
+
HO
H
OCH3
OCH3
+
H+
+ HOH
HOCH3
OCH3
HOCH3
+
CH3O
H
OCH3
CH3O
OCH3
+
Chapter 9
27
Oxidation of Aldehydes
Easily oxidized to carboxylic acids.
Chapter 18
28
Cyclic Acetals
• Addition of a diol produces a cyclic acetal.
• Sugars commonly exist as acetals or
hemiacetals.
CH2 CH2
O
O
O
+
CH2
HO
CH2
OH
Chapter 9
29
Tollens Test
• Add ammonia solution to AgNO3 solution
until precipitate dissolves.
• Aldehyde reaction forms a silver mirror.
O
R C H + 2
+
NH3)2
_
+
3 OH
+
Ag(NH3)2
_
+
3 OH
O
H2O
O
H2O
2 Ag + R C O
2 Ag + R C O
_
+
_
+
4 NH3 + 2 H2O
=>
Chapter 18
30
4
SILVER MIRROR
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
32
Catalytic Hydrogenation
• Widely used in industry.
• Raney nickel, finely divided Ni powder
saturated with hydrogen gas.
• Pt and Rh also used as catalysts.
O
OH
Raney Ni
Chapter 18
H
33
Tautormers
Constitutional 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
O
Name
H3C
CH
CH
a.
b.
c.
d.
Cis-2-pentenal
Cis-2-pentanal
Trans-2-pentenal
Trans-2-pentanal
C
CH2
H
Answer
a.
b.
c.
d.
Cis-2-pentenal
Cis-2-pentanal
Trans-2-pentenal
Trans-2-pentanal
The aldehyde is in position one. The
double bond is trans.
Name
H3C
CH2
O
O
C
C
CH2
a. 2-Oxobutanoic acid
b.2-Butanone-1-carbaldehyde
c. 2-Oxopentanoic acid
d.3-Oxopentanoic acid
OH
Answer
a. 2-Oxobutanoic acid
b.2-Butanone-1-carbaldehyde
c. 2-Oxopentanoic acid
d.3-Oxopentanoic acid
The carbon in the carboxylic acid is
position one.
Identify the chemical name for
acetone.
a. Methanal
b.Ethanal
c. Propanone
d.Butanone
Answer
a. Methanal
b.Ethanal
c. Propanone
d.Butanone
Acetone is called propanone or
dimethyl ketone.
1. CH3CH2MgCl
2. H3O+
O
C
H3C
a. 2-Propanone
b.2-Butanone
c. 2-Pentanone
d.3-Pentanone
H
3. Na2Cr2O7, H2SO4
Answer
a. 2-Propanone
b.2-Butanone
c. 2-Pentanone
d.3-Pentanone
2-Butanone is formed in the Grignard
reaction. The secondary alcohol is oxidized
to a ketone with sodium dichromate.
O
1. CH3CH2Li
C
H3C
a. 2-Propanone
b.2-Butanone
c. 2-Pentanone
d.3-Pentanone
OH
2. H3O+
Answer
a. 2-Propanone
b.2-Butanone
c. 2-Pentanone
d.3-Pentanone
The ethyl group adds to the carbonyl carbon.
O
2 CH3CH2OH
C
H3C
CH3
H+
a. 2,2-Diethoxypropane
b.2-Ethoxy-2-propanol
c. Propane-2,2-diol
d.2-Ethoxypropane
Answer
a. 2,2-Diethoxypropane
b.2-Ethoxy-2-propanol
c. Propane-2,2-diol
d.2-Ethoxypropane
Two molecules of ethanol are added to
the carbonyl, with loss of water.
O
-
1. Ag(NH3)2, OH
H3C
C
CH2
H
+
2. H
a. 1-Propanol
b.Propanoic acid
c. Propane-1,1-diol
d.1-Hydroxypropanoic acid
Answer
a. 1-Propanol
b.Propanoic acid
c. Propane-1,1-diol
d.1-Hydroxypropanoic acid
The Tollens reagent reduces an
aldehyde to a carboxylic acid.
O
H3C
NaBH4
C
CH2
CH3
a. 2-Butanone
b.2-Butanol
c. 2-Hexanone
d.Butane
CH3CH2OH
Answer
a. 2-Butanone
b.2-Butanol
c. 2-Hexanone
d.Butane
Butanone is reduced to 2-butanol.
End of Chapter 9
Chapter 9
52