1. Chapter 17 Aldehydes and Ketones

2. 17.1 Nomenclature 2

3. Nomenclature of Aldehydes
4,4-dimethylpentanal
5-hexenal O
HCCHCH
2-phenylpropanedial 4

4. Nomenclature of Aldehydes
when named as
a substituent
when named
as a suffix
formyl group
carbaldehyde
carboxaldehyde 5

5. Substitutive Nomenclature of Ketones
CH3CH2CCH2CH2CH3 O
CH3CHCH2CCH3 O
CH3
3-hexanone
4-methyl-2-pentanone
H3C O
4-methylcyclohexanone 6

6. Functional Class Nomenclature of Ketones
CH3CH2CCH2CH2CH3 O O
CH2CCH2CH3
ethyl propyl ketone
benzyl ethyl ketone CH
CH2 O
H2C
CHC
divinyl ketone 6

7. 17.2 Structure and Bonding: The Carbonyl Group

8. Structure of Formaldehyde
planar
bond angles: close to 120°
C=O bond distance: pm 8

9. The Carbonyl Group very polar double bond O 1-butene propanal
dipole moment = 0.3D
dipole moment = 2.5D 9

10. Carbonyl group of a ketone is more stable than that of an aldehyde
heat of combustion
2475 kJ/mol O
2442 kJ/mol
Alkyl groups stabilize carbonyl groups the same way they stabilize carbon-carbon double bonds, carbocations, and free radicals. 10

11. Spread is greater for aldehydes and ketones than for alkenes
Heats of combustion of C4H8 isomeric alkenes
CH3CH2CH=CH kJ/mol
cis-CH3CH=CHCH kJ/mol
trans-CH3CH=CHCH kJ/mol
(CH3)2C=CH kJ/mol O H
2475 kJ/mol O
2442 kJ/mol 11

12. Resonance Description of Carbonyl Group••
• • C O + – ••
• •
nucleophiles attack carbon; electrophiles attack oxygen 12

13. Bonding in Formaldehyde
Carbon and oxygen are sp2 hybridized 8

14. Bonding in Formaldehyde
The half-filled p orbitals on carbon and oxygen overlap to form a p bond 8

15. 17.3 Physical Properties 14

16. Aldehydes and ketones have higher boiling than alkenes, but lower boiling points than alcohols.
More polar than alkenes, but cannot form intermolecular hydrogen bonds to other carbonyl groups O
49°C OH
97°C 12

17. 17.4 Sources of Aldehydes and Ketones14

18. Many aldehydes and ketones occur naturally
2-heptanone (component of alarm pheromone of bees) 15

19. Many aldehydes and ketones occur naturally
trans-2-hexenal (alarm pheromone of myrmicine ant) 15

20. Many aldehydes and ketones occur naturally
citral (from lemon grass oil) 15

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 already studied provide efficient synthetic routes to aldehydes and ketones. 17

22. aldehydes from carboxylic acids
What about..?
aldehydes from carboxylic acids C O R OH H C O R 18

23. aldehydes from carboxylic acids
What about..?
aldehydes from carboxylic acids C O R OH H C O R
1. LiAlH4
PDC, CH2Cl2
2. H2O
RCH2OH 18

24. benzaldehyde from benzoic acid
Example
benzaldehyde from benzoic acid
COH O CH O
1. LiAlH4
CH2OH
PDC CH2Cl2
2. H2O
(81%)
(83%) 18

25. ketones from aldehydes
What about..?
ketones from aldehydes C O R H R' C O R 18

26. ketones from aldehydes
What about..?
ketones from aldehydes C O R H R' C O R
1. R'MgX OH
PDC, CH2Cl2
2. H3O+
RCHR' 18

27. 3-heptanone from propanal
Example
3-heptanone from propanal O O
CH3CH2C(CH2)3 CH3 C
CH3CH2 H
(57%)
1. CH3(CH2)3MgX
H2CrO4
2. H3O+
CH3CH2CH(CH2)3 CH3 OH 18