Chapter 13. Aldehydes and Ketones
Learning objectives:
1. Provide both IUPAC and common names for aldehydes and ketones.
2. Recognize the physical properties of for aldehydes and ketones.
3. Write the general electron-pushing (arrow-pushing) mechanisms for the nucleophilic
addition to a carbonyl group with the following nucleophiles: Grignard reagent, alcohol,
water, and amine.
4. Write the general electron-pushing (arrow-pushing) mechanism for the tautomerization
between keto and enol, and explain the observed racemization at the α-carbon.
5. Recognize the reagents for the transformation from aldehyde to carboxylic acid.
6. Recognize the reagents and conditions used for the reduction of aldehyde and ketone to
alcohol.
7. Utilize reductive amination for the synthesis of amines.
8. Recognize the reagents and conditions used for α-halogenation.
Sections to be covered (in the order of delivery):
13.1
13.2
13.3
13.4
13.5
13.6
13.7
13.8
13.9
13.10
13.11
Introduction#
Structure and Bonding
Nomenclature
Physical Properties
Reactions*
Addition of Grignard Reagents*
Addition of Alcohols*
Addition of Ammonia and Amines*
Keto-Enol Tautomerism*
Oxidation
Reduction
* Sections that will be focused
#
Sections that will be skipped
Recommended additional problems
13.12 – 13.30, 13.33, 13.35 – 13.39, 13.43
1
13.2
Structure and Bonding
O
O
R
H
H
13.3
Nomenclature
O
R
H
O
O
R'
H
H
O
O
H
H
O
H
H
HO
O
H
O
H
O
Cl
H
OCH2CH3
O
O
OCH2CH3
CHO
2
O
H
H
O
O
O
O
O
O
O
O
O
O
CH3
13.4
O
Physical Properties
3
13.5
Reactions
A. In basic condition
O
O
R
H (R)
Nu
O
H
R
H(R)
Nu
R
H(R)
tetrahedral
intermediate
Nu (
Z)
B. In acidic condition
H
B
B
+
H
O
R
O
H (R)
R
H
O
H
H (R)
4
R
B
H(R)
13.6
Addition of Grignard Reagents
A. Formation and Structure of Organomagnesium Compounds
B. Reaction with Protic Acids
C. Addition of Grignard Reagents to Aldehydes and Ketones
5
13.7
Addition of Alcohols
A. Formation of Acetals and Ketals with Water
O
HO
R
OH
H (R)
R
H(R)
H2O
(i) Consideration of pKa
(ii) Stability consideration
6
B. Addition of Alcohol: Formation of Hemiacetal, Acetal, Hemiketal, and Ketal)
O
R'O
R'O
R
OR'
OH
H
R
H
H
R
HOR'
(2 equivalents)
H2O
O
R'O
R'O
R
OR'
OH
R
R
R
R
R
HOR'
(2 equivalents)
H2O
C. Mechanism
7
D. Acetals or Ketals as the Carbonyl-Protecting Groups
(i) Stability of Acetals and Ketals
(ii) Example
O
O
+
O
+
HOCH2CH2OH
H2O
(i)
OH
OH
O
O
H
+
O
O
?
H
Br
H
8
13.8
Addition of Ammonia and Amines
A. Formation of Imines
O
NR'
R
H
H+
R
H
+
H2NR'
+
H2O
(i) Mechanism
(ii) Why optimal pH is necessary for the formation of imine?
9
B. Reductive Amination of Aldehydes and Ketones
13.9
Keto-Enol Tautomerism
A. Keto and Enol Forms
OH
O
R
CH2R'
R
10
CHR'
B. Racemization at an α-Carbon
O
C
H3C
H
C
CH3
(R)-3-Phenyl-2-butanone
Mechanism and Consequence of tautomerization:
11
C. α-Halogenation
O
O
X2 (Cl2, Br2, I2)
H3O+
CH3
CH2
X
13.10 Oxidation
A. Oxidation of Aldehydes to Carboxylix Acids
(i) Examples
H2CrO4
O
O
H2CrO4
(ii) Tollens’ Reagent (Silver-mirror Test)
AgNO3
+
Ag(NH3)2+ NO3-
2 NH3
O
O
H
+
O-
2 Ag(NH3)2+
12
+
2 Ag
+
4 NH3
B. Oxidation of Ketones to Carboxylic Acids (Skipped)
13.11 Reduction
A. Catalytic Reduction
H2
Raney Ni
O
H
H2
Raney Ni
H
H2
Pt
O
O
(i) Commonly Used Metal Catalysts: Pd, Pt [Pt(0), Pt(II)], Ni (Raney Nickel), Rh
B. Metal Hydride Reduction
1) NaBH4
2) H3O+
O
H
1) NaBH4
2) H3O+
O
1) LiAlH4
2) H3O+
O
H
1) LiAlH4
2) H3O+
O
13