Organic Chemistry, 5th Edition
L. G. Wade, Jr.
Chapter 18
Ketones and Aldehydes
Jo Blackburn
Richland College, Dallas, TX
Dallas County Community College District
2003, Prentice Hall
Carbonyl Compounds
=>
Chapter 18
2
Carbonyl Structure
• Carbon is sp2 hybridized.
• C=O bond is shorter, stronger, and
more polar than C=C bond in alkenes.
=>
Chapter 18
3
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 18
4
Examples
O
O
CH3
C CH CH3
CH3
3-methyl-2-butanone
Br
3-bromocyclohexanone
O
CH3
C CH CH2OH
CH3
4-hydroxy-3-methyl-2-butanone
=>
Chapter 18
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 18
6
Examples
CH3
CH2
CH3
O
CH CH2
C H
3-methylpentanal
CHO
2-cyclopentenecarbaldehyde
=>
Chapter 18
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
3-methyl-4-oxopentanal
CHO
3-formylbenzoic acid
Chapter 18
=>
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 18
9
Historical Common
Names
C
O
CH3
O
CH3
C CH3
acetophenone
acetone
O
C
benzophenone
=>
Chapter 18
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.
=>
Chapter 18
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 18
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 18
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
H2O
formaldehyde,
b.p. -21C
trioxane, m.p. 62C
HO
OH
H C
H
formalin
=>
Chapter 18
14
IR Spectroscopy
•
•
•
•
Very strong C=O stretch around 1710 cm-1.
Conjugation lowers frequency.
Ring strain raises frequency.
Additional C-H stretch for aldehyde: two
absorptions at 2710 cm-1 and 2810 cm-1.
=>
Chapter 18
15
1H
NMR Spectroscopy
=>
Chapter 18
16
13C
NMR Spectroscopy
Chapter 18
17
=>
MS for 2-Butanone
=>
Chapter 18
18
MS for Butyraldehyde
=>
Chapter 18
19
McLafferty
Rearrangement
• Loss of alkene (even mass number)
• Must have -hydrogen
=>
Chapter 18
20
UV Spectra,   *
• C=O conjugated with another double bond.
• Large molar absorptivities (> 5000)
=>
Chapter 18
21
UV Spectra, n  *
• Small molar absorptivity.
• “Forbidden” transition occurs less frequently.
=>
Chapter 18
22
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 18
23
Synthesis Review
• Oxidation
2 alcohol + Na2Cr2O7  ketone
1 alcohol + PCC  aldehyde
• Ozonolysis of alkenes.
R'
H
C C
R
R''
R'
H
1) O3
2) (CH3)2S
C O
R
+ O C
R''
=>
Chapter 18
24
Synthesis Review (2)
• Friedel-Crafts acylation
Acid chloride/AlCl3 + benzene  ketone
CO + HCl + AlCl3/CuCl + benzene 
benzaldehyde (Gatterman-Koch)
• Hydration of terminal alkyne
Use HgSO4, H2SO4, H2O for methyl ketone
Use Sia2BH followed by H2O2 in NaOH for
aldehyde.
=>
Chapter 18
25
Synthesis Using
1,3-Dithiane
• Remove H+ with n-butyllithium.
BuLi
S
S
H
H
S
_
S
H
• Alkylate with primary alkyl halide,
then hydrolyze.
O
+
H , HgCl2
CH3CH2Br
S
_
H
S
S
H
S
H2O
C
H
CH2CH3
=>
CH2CH3
Chapter 18
26
Ketones from
1,3-Dithiane
• After the first alkylation, remove the
second H+, react with another primary
alkyl halide, then hydrolyze.
CH3Br
BuLi
S
H
S
CH2CH3
S
_
S
CH2CH3
O
+
H , HgCl2
S
CH3
S
H2O
C
CH3
CH2CH3
CH2CH3
=>
Chapter 18
27
Ketones from
Carboxylates
• Organolithium compounds attack the
carbonyl and form a diion.
• Neutralization with aqueous acid
produces an unstable hydrate that loses
water to form a ketone.
O
C
_
O Li +
_ +
O Li
_ +
C O Li
CH3
H3O
+
OH
O
C OH _
H2O
CH3
C
CH3
CH3Li
=>
Chapter 18
28
Ketones from Nitriles
• A Grignard or organolithium reagent
attacks the nitrile carbon.
• The imine salt is then hydrolyzed to
form a ketone.
N MgBr
C N
CH3CH2MgBr +
C
ether
CH2CH3
O
H3O
+
C
CH2CH3
=>
Chapter 18
29
Aldehydes from
Acid Chlorides
Use a mild reducing agent to prevent
reduction to primary alcohol.
O
CH3CH2CH2C
O
Cl
LiAlH(O-t-Bu)3
CH3CH2CH2C
H
=>
Chapter 18
30
Ketones from
Acid Chlorides
Use lithium dialkylcuprate (R2CuLi),
formed by the reaction of 2 moles of
R-Li with cuprous iodide.
2 CH3CH2CH2Li
CuI
(CH3CH2CH2)2CuLi
O
(CH3CH2CH2)2CuLi +
CH3CH2C Cl
O
CH3CH2C CH2CH2CH3
=>
Chapter 18
31
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
32
=>
Wittig Reaction
• Nucleophilic addition of phosphorus ylides.
• Product is alkene. C=O becomes C=C.
Chapter 18
33
=>
Phosphorus Ylides
• Prepared from triphenylphosphine and an
unhindered alkyl halide.
• Butyllithium then abstracts a hydrogen
from the carbon attached to phosphorus.
Ph3P
+
Ph3P
+ CH3CH2Br
CH2CH3
_
+
Ph3P
BuLi
+
Ph3P
ylide
Chapter 18
CH2CH3 Br
_
CHCH3
=>
34
Mechanism for Wittig
• The negative C on ylide attacks the
positive C of carbonyl to form a betaine.
• Oxygen combines with phosphine to
form the phosphine oxide. +
+
Ph3P
_
Ph3P
H3C
H C C CH3
CH3 Ph
C O
CHCH3
Ph
+
Ph3P
_
O
H C C CH3
CH3 Ph
Ph3P
O
O
H C C CH3
CH3 Ph
Chapter 18
Ph3P
H
H3C
O
C C
CH3
Ph
=>
35
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
O
CH3
C
CH3
C
H
HO
+ H2O
OH
CH3
Chapter 18
H
K = 2000
OH
C
CH3
K = 0.002
=>
36
Addition of HCN
• HCN is highly toxic.
• Use NaCN or KCN in base to add
cyanide, then protonate to add H.
• Reactivity formaldehyde > aldehydes >
ketones >> bulky ketones.
O
CH3CH2
C
HO
CH3
+ HCN
Chapter 18
CH3CH2
CN
C
CH3
37
=>
Formation of Imines
• Nucleophilic addition of ammonia or
primary amine, followed by elimination
of water molecule.
• C=O becomes C=N-R
CH3
H3C
RNH2
C O
Ph
R
CH3
R
_
C
H2N
O
+ Ph
R
Chapter 18
CH3
N C OH
H
Ph
CH3
N C
Ph
N C OH
H
Ph
R
=>38
pH Dependence
• Loss of water is acid catalyzed, but acid
destroys nucleophiles.
• NH3 + H+  NH4+ (not nucleophilic)
• Optimum pH is around 4.5
=>
Chapter 18
39
Other Condensations
Chapter 18
40
=>
Addition of Alcohol
=>
Chapter 18
41
Mechanism
• Must be acid-catalyzed.
• Adding H+ to carbonyl makes it more
reactive with weak nucleophile, ROH.
• Hemiacetal forms first, then acidcatalyzed loss of water, then addition of
second molecule of ROH forms acetal.
• All steps are reversible.
=>
Chapter 18
42
Mechanism for
Hemiacetal
O
+ OH
+
H+
H
OH
+
OH
HO
HOCH3
HO
OCH3
+
HOCH3
Chapter 18
OCH3
+
+ H2OCH3
43
=>
Hemiacetal to Acetal
HO
OCH3
+
HO
H
OCH3
OCH3
+
H+
+ HOH
HOCH3
OCH3
HOCH3
+
CH3O
H
OCH3
CH3O
OCH3
+
=>
Chapter 18
44
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 18
45
Acetals as
Protecting Groups
• Hydrolyze easily in acid, stable in base.
• Aldehydes more reactive than ketones.
O
O
CH2
CH2
OH
HO
C
H
+
H
C
O
O
O
=>
Chapter 18
46
Selective Reaction
of Ketone
• React with strong nucleophile (base)
• Remove protective group.
+
_
MgBr O CH
3
O
HO
CH3MgBr
C
O
O
H3O
C
O
O
CH3
+
C
H
O
=>
Chapter 18
47
Oxidation of Aldehydes
Easily oxidized to carboxylic acids.
=>
Chapter 18
48
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
49
4
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
50
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
H
=>
Chapter 18
51
Deoxygenation
• Reduction of C=O to CH2
• Two methods:
Clemmensen reduction if molecule is
stable in hot acid.
Wolff-Kishner reduction if molecule is
stable in very strong base.
=>
Chapter 18
52
Clemmensen Reduction
O
C
CH2CH3
Zn(Hg)
CH2CH2CH3
HCl, H2O
O
CH2
C
Zn(Hg)
H
CH2
CH3
HCl, H2O
=>
Chapter 18
53
Wolff-Kisher Reduction
• Form hydrazone, then heat with strong
base like KOH or potassium t-butoxide.
• Use a high-boiling solvent: ethylene
glycol, diethylene glycol, or DMSO.
CH2
C H
H2N NH2
CH2
O
C H
NNH2
KOH
heat
CH2
CH3
=>
Chapter 18
54
End of Chapter 18
Chapter 18
55