Chapter 17 Aldehydes and Ketones

1
Chapter 17Aldehydes and Ketones
2
17.1Nomenclature
3
Nomenclature of Aldehydes
4,4-dimethylpentanal
5-hexenal
2-phenylpropanedial
4
Nomenclature of Aldehydes
when named as a suffix
when named as a substituent
formyl group
carbaldehyde
carboxaldehyde
5
Substitutive Nomenclature of Ketones
3-hexanone
4-methyl-2-pentanone
4-methylcyclohexanone
6
Functional Class Nomenclature of Ketones
ethyl propyl ketone
benzyl ethyl ketone
divinyl ketone
7
17.2Structure and BondingThe Carbonyl Group
8
Structure of Formaldehyde

• planar
• bond angles close to 120
• CO bond distance 122 pm

9
The Carbonyl Group

• very polar double bond

O
1-butene
propanal
dipole moment 2.5D
dipole moment 0.3D
10
Carbonyl group of a ketone is morestable than
that of an aldehyde
heat of combustion
2475 kJ/mol
2442 kJ/mol

• Alkyl groups stabilize carbonyl groups the
  sameway they stabilize carbon-carbon double
  bonds,carbocations, and free radicals.

11
Spread is greater foraldehydes andketones than
for alkenes

• Heats of combustion ofC4H8 isomeric alkenes
• CH3CH2CHCH2 2717 kJ/mol
• cis-CH3CHCHCH3 2710 kJ/mol
• trans-CH3CHCHCH3 2707 kJ/mol
• (CH3)2CCH2 2700 kJ/mol

2475 kJ/mol
2442 kJ/mol
12
Resonance Description ofCarbonyl Group

• nucleophiles attack carbon electrophiles
  attack oxygen

13
Bonding in Formaldehyde
Carbon and oxygen are sp2 hybridized
14
Bonding in Formaldehyde
The half-filledp orbitals oncarbon andoxygen
overlapto form a p bond
15
17.3Physical Properties
16
Aldehydes and ketones have higher boilingthan
alkenes, but lower boiling points than alcohols.
boiling point
6C

• More polar than alkenes, but cannot form
  intermolecular hydrogen bonds to other carbonyl
  groups

49C
97C
17
17.4Sources of Aldehydes and Ketones
18
Many aldehydes and ketones occur naturally

2-heptanone(component of alarm pheromone of bees)
19
Many aldehydes and ketones occur naturally
O
H
trans-2-hexenal (alarm pheromone of myrmicine
ant)
20
Many aldehydes and ketones occur naturally
O
H
citral (from lemon grass oil)
21
Synthesis of Aldehydes and Ketones

• from alkenes
• ozonolysis
• from alkynes
• hydration (via enol)
• from arenes
• Friedel-Crafts acylation
• from alcohols
• oxidation

A number of reactions alreadystudied
provideefficient syntheticroutes to aldehydes
and ketones.
22
What about..?

• aldehydes from carboxylic acids

23
What about..?

• aldehydes from carboxylic acids

1. LiAlH4
PDC, CH2Cl2
2. H2O
RCH2OH
24
Example

• benzaldehyde from benzoic acid

1. LiAlH4
PDCCH2Cl2
2. H2O
(83)
(81)
25
What about..?

• ketones from aldehydes

26
What about..?

• ketones from aldehydes

1. R'MgX
OH
PDC, CH2Cl2
2. H3O
RCHR'
27
Example

• 3-heptanone from propanal

O
C
CH3CH2
H
(57)
1. CH3(CH2)3MgX
H2CrO4
2. H3O