Aldehydes and Ketones
Nomenclature
Nucleophilic Addition
to the
Carbonyl Group
IUPAC Nomenclature of Aldehydes
O
O
H
H
O
O
HCCHCH
Base the name on the
chain that contains
the carbonyl group
and replace the -e
ending of the
hydrocarbon with -al.
-al.
IUPAC Nomenclature of Aldehydes
IUPAC Nomenclature of Aldehydes
O
O
H
H
4,4-dimethylpentan
al
4,4-dimethylpentanal
O
O
HCCHCH
5-hexen
al
5-hexenal
or hex-5-enal
hex-5-enal
O
when named as
a substituent
formyl group
2-phenylpropane
dial
2-phenylpropanedial
(keep the -e ending
before -dial)
-dial)
C
H
when named
as a suffix
carbaldehyde or
carboxaldehyde
Substitutive IUPAC Nomenclature of Ketones
Question
O
• What is the correct IUPAC name of the aldehyde at the right?
•
•
•
•
A)
B)
C)
D)
CH3CH2 CCH2 CH2CH3
Base the name on the chain
that contains the carbonyl group
-one.
O and replace -e with -one.
Number the chain in the
direction that gives the lowest
number to the carbonyl carbon.
H3 C
Substitutive IUPAC Nomenclature of Ketones
O
Functional Class IUPAC Nomenclature of Ketones
O
3-hexan
one
3-hexanone
or Hexan-3-one
Hexan-3-one
H3 C
CH3CHCH2CCH3
O
CH3CH2 CCH2 CH2CH3
4-methyl-2pentanone
one
4-methyl-2-pentan
or 4-methylpentan-2-one
4-methylpentan-2-one
O
H2 C
CHC CH
Functional Class IUPAC Nomenclature of Ketones
O
CH3CH2 CCH2 CH2CH3
ethyl propyl ketone
CH2
CH2
List the groups
attached to the
carbonyl separately in
alphabetical order, and
add the word ketone.
ketone.
Question
• What is the IUPAC name for the ketone shown below?
CH2CCH2CH3
benzyl ethyl ketone
O
CHC CH
CH2CCH2CH3
CH3
4-methylcyclohexanone
4-methylcyclohexanone
H2 C
O
O
O
CH3CHCH2CCH3
CH3
2,3-dihydroxypropanol
1,2-dihydroxypropanal
2,3-dihydroxypropanal
2,3-propanediol-1-aldehyde
CH3CH2 CCH2 CH2CH3
O
divinyl ketone
•
•
•
•
A)
B)
C)
D)
5-ethyl-2-methyl-3-hexanone
2,5-dimethyl-3-heptanone
3,6-dimethyl-5-heptanone
2-ethyl-5-methyl-5-hexanone
Question
•
A compound (C7H14O) has a strong peak in its IR spectrum
at 1710 cm-1. Its 1H-NMR spectrum consists of 3 singlets in
the ratio 9:3:2 at δ1.0, δ2.1, and δ2.3, respectively.
The Carbonyl Group
Structure, Bonding
Identify this compound.
•
•
•
•
A)
B)
C)
D)
3-heptanone
2,2-dimethyl-3-pentanone
4,4-dimethyl-2-pentanone
2,4-dimethyl-3-pentanone
Carbonyl Group of a Ketone is More
Stable than that of an Aldehyde
heat of combustion
O
H
2475 kJ/mol
Spread is Greater for
Aldehydes and
Ketones than for Alkenes
O
CH3CH2 CH=CH2
2717 kJ/mol
H
2475 kJ/mol
2442 kJ/mol
cis-CH
cis-CH3 CH=CHCH3
2710 kJ/mol
trans-CH
trans-CH3 CH=CHCH3
2707 kJ/mol
O
Alkyl groups stabilize carbonyl groups the same
way they stabilize carbon-carbon double bonds,
carbocations, and free radicals.
Heats of combustion of
C4 H8 isomeric alkenes
O
2442 kJ/mol
(CH3 )2C=CH2
2700 kJ/mol
Resonance Description of
Carbonyl Group
••
•• –
O ••
•• O ••
C
C
+
Nucleophiles attack carbon;
electrophiles attack oxygen.
Synthesis
Aldehydes & Ketones
Synthesis of Aldehydes and Ketones
Question
from alkenes
A number of
reactions already
studied provide
efficient synthetic
routes to
aldehydes and
ketones.
ketones.
• What combination of reagents will transform 1-butyne into 2butanone?
ozonolysis
from alkynes
hydration (via enol)
from arenes
•
•
•
•
A)
B)
C)
D)
1. O3 2. H2O, Zn
K2Cr2O7, H2SO4
H2SO4, HgSO4
OsO4 (cat), (CH3)3COOH, (CH3) 3OH, HO-
Friedel-Crafts acylation
from alcohols
oxidation
Example
Reduction & Oxidation
aldehydes from carboxylic acids
O
R
C
Benzaldehyde from benzoic acid
O
R
OH
1. LiAlH4
2. H2O
C
H
PCC or
PDC, CH2 Cl2
RCH2OH
O
O
COH
CH
1. LiAlH4
2. H2O
CH2OH
(81%)
Reduction
Grignard & Oxidation
aldehydes from carboxylic acid esters
O
R
C
1. DIBAL-H
2. H2O
Ketones from aldehydes
O
O
(Diisobutyl aluminum hydride)
OR’
OR’
(83%)
PCC or
PDC
CH2Cl2
R
C
or from nitriles R-CN with DIBAL-H
H
R
1. R'MgX
2. H3O+
C
O
R
H
OH
RCHR'
RCHR'
C
R'
PCC or
PDC, CH2 Cl2
Example
Question
3-heptanone from propanal
• Which combination of reagents will produce 2-hexanone as
the major organic product?
•
•
•
A)
2-hexanol + PCC in CH2Cl2
B)
1-hexene + H2O, H2SO4, HgSO4
C)
pentanal + methylmagnesium bromide followed by
H3O+
•
D)
All of the above (a-c) will produce 2-hexanone as
the major product.
O
CH3CH2
C
O
CH3CH2 C(CH2)3 CH3
H
(57%)
1. CH3 (CH2 )3MgX
2. H3O+
H2 CrO4
OH
CH3CH2 CH(CH
CH(CH2 )3 CH3
Question
• An alcohol with a molecular formula C7H16O was treated with
chromic acid. The product produced 4 signals in its 13C-NMR
spectrum: one at 210 ppm and 3 others below 50 ppm.
Identify the ketone.
•
A)
4-heptanone
•
B)
2,4-dimethyl-3-pentanone
•
C)
4,4-dimethyl-2-pentanone
•
D)
5-methyl-3-hexanone
Reactions of Aldehydes and
Ketones
Reactions of Aldehydes and Ketones
Question
•
Which compound will be isolated from the synthetic
sequence shown below?
•
A)
B)
•
C)
D)
Reduction of C=O to CH2
Clemmensen reduction
Wolff-Kishner reduction
Reduction of C=O to CHOH
Addition of Grignard and organolithium reagents
Question
Aldehydes and ketones react with nucleophiles to form
addition products: nucleophile addition reactions
• When a nucleophile encounters a ketone, the site of attack is
•
A)
the carbon atom of the cabonyl.
•
B)
the oxygen atom of the carbonyl.
•
C)
both the carbon and oxygen atoms, with
equal probability.
•
D)
No attack occurs--ketones do not react with
nucleophiles.
Hydration of Aldehydes and Ketones
C
Hydration of Aldehydes and
Ketones
••
H2 O
••
HO
••
C
••
O
••
H
Equilibrium Constants and Relative Rates
of Hydration
Substituent Effects on Hydration Equilibria
C=O
hydrate
K
%
Relative
rate
CH2=O
CH2 (OH)2
2300
>99.9
2200
compared to H
CH3CH=O
CH3 CH(OH)2
1.0
50
1.0
electronic:
alkyl groups stabilize
reactants
(CH3)3 CCH=O
(CH3)3CCH(OH)2 0.2
17
0.09
(CH3)2 C=O
(CH3)2C(OH)2
0.14
0.0018
steric:
alkyl groups crowd
product
OH
O
+ H2 O
C
R
O ••
R
R'
C
OH
R'
0.0014
Equilibrium Can Favor a Hydrate
Substituent Effects on Hydration Equilibria
(But not very often)
OH
O
Only when the carbonyl group is destabilized
+ H2 O
C
• alkyl groups stabilize C=O
C
R
R
R
R
OH
• electron-withdrawing groups destabilize C=O
R = CH3: K = 0.0014
R = CF3: K = 22,000
Mechanism of Hydration (base)
Mechanism of Hydration (base)
Step 1:
H
–
•O•
• •• •
Step 2:
+
C
••
O ••
HO
••
••
C
•• –
O ••
••
HO
••
••
••
••
C
OH
••
Mechanism of Hydration (acid)
Step 1:
O ••
••
+
H
H
–
+ •• O ••
O ••
••
••
Mechanism of Hydration (acid)
Step 2:
H
C
••
H
H
HO
•• –
O ••
C
••
O•
+ •
H
C
+
OH
••
H
+
H
•O•
• •
•O•
• •
H
H
+
C
+
OH
H
•O
• +
••
H
C
••
OH
••
Mechanism of Hydration (acid)
Question
Step 3:
H
••
+O
• Which one of the compounds below has the fastest hydration
rate?
H
H
C
H
H
•
A)
B)
•
C)
D)
••
H
+
••
•O
•
••
O
H
•O
• +
••
OH
H
••
C
••
OH
••
Cyanohydrin Formation
Cyanohydrin Formation
C
•N
•
O •• + HCN
••
Cyanohydrin Formation
C
••
O
C
••
Cyanohydrin Formation
H
•N
•
–
C ••
C
O ••
••
•N
•
C
C
•• –
O ••
••
H
O ••
+
H
H
•N
•
C
C
••
O
••
H
• O ••
•
H
H
Example
Example
Cl
Cl
Cl
O
NaCN, water
Cl
CH
O
OH
NaCN, water
CH3CCH3
then H2 SO4
CHCN
then H2SO4
OH
CH3CCH3
CN
(77-78%)
2,4-Dichlorobenzaldehyde
cyanohydrin (100%)
Acetone cyanohydrin is used in the synthesis
of methacrylonitrile
Some reactions of aldehydes and ketones progress
beyond the nucleophilic addition stage
Acetal formation
Acetal Formation
Imine formation
Enamine formation
Compounds related to imines
The Wittig reaction
Recall Hydration of Aldehydes and Ketones
R
C
O ••
••
R'
HOH
R
••
HO
••
C
R'
••
O
••
H
Alcohols Under Analogous Reaction
with Aldehydes and Ketones
Hemiacetal reacts further in acid to yield an acetal
R
R
••
R"O
O ••
C
••
••
••
C
••
R'
R'
ROH,
ROH, H+
R"OH
R"OH
R
••
R"O
C
••
R
••
O
••
H
Product is called
a hemiacetal.
hemiacetal.
••
R"O
••
R'
• The structure shown at the right would be best classified as
a(n)
A)
B)
C)
D)
••
C
O
••
Product is called
a hemiacetal.
hemiacetal.
H
R'
Question
•
•
•
•
Product is called
an acetal.
acetal.
OR
acetal.
hemiacetal.
hydrate.
cyanohydrin.
Example
O
CH + 2CH3CH2 OH
HCl
CH(O
CH(OCH2 CH3)2
+ H2O
Benzaldehyde diethyl acetal (66%)
Diols Form Cyclic Acetals
In general:
O
CH3(CH2)5CH
+
HOCH2 CH2OH
benzene
p-toluenesulfonic acid
H2 C
CH2
O
O
+ H2 O
C
(81%)
H
(CH2 )5CH3
Position of equilibrium is usually unfavorable
for acetal formation from ketones.
ketones.
Important exception:
Cyclic acetals can be prepared from ketones.
ketones.
Example
Question
O
C6 H5CH2 CCH3 +
• What is the product of the reaction between benzaldehyde and 1,3propanediol?
HOCH2 CH2OH
benzene
p-toluenesulfonic acid
(78%)
H2 C
CH2
O
O
• A)
B)
• C)
D)
+ H2 O
C
CH3
C6 H5CH2
Hydrolysis of Acetals
OR"
R
C
O
C
R' + H2O
R
OR"
mechanism:
+
R'
2R"O
2R"O H
Acetals as Protecting Groups
reverse of acetal formation;
hemiacetal is intermediate
application:
aldehydes and ketones can be
"protected" as acetals.
acetals.
Example
The conversion shown cannot be carried out
directly...
O
CH3CCH2CH2 C
CH
1. NaNH2
2. CH3 I
O
CH3CCH2CH2 C
CCH3
because the carbonyl group and the
carbanion are incompatible functional
groups.
O
CH3CCH2CH2 C
C:
–
Example: Protect
Strategy
O
CH3CCH2CH2 C
1) protect C=O
CH +
HOCH2 CH2OH
benzene
p-toluenesulfonic acid
2) alkylate
3) restore C=O
H2 C
CH2
O
O
C
CH2CH2 C
CH3
Example: Alkylate
H2 C
Example: Deprotect
CH2
H2 C
O
O
O
C
CH2CH2 C
CH3
CH3
O
O
CH2CH2 C
HOCH2 CH2OH
C
CH2CH2 C
CH
What reagent and/or reaction conditions would you choose
to bring about the following conversion?
A)
B)
C)
D)
H2 O
1. LiAlH4; 2. H2O
H2O, H2SO4, heat
H2O, NaOH, heat
PCC, CH2Cl2
CCH3
HCl
O
Question
•
•
•
•
O
CH2
CH3
•
CH2
C
CCH3
H2 C
1. NaNH2
2. CH3 I
CH
+
CH3CCH2CH2 C
(96%)
CCH3