1. Chemeketa Community College
Aldehydes and Ketones
Chapter 23
Larry Emme
Chemeketa Community College

2. Structures of Aldehydes & Ketones

3. Both aldehydes and ketones contain a carbonyl ( C=O) group.
aromatic
aromatic
aromatic
aromatic

4. In a linear expression, the aldehyde group is often written as:
CHO

5. In the linear expression of a ketone, the carbonyl group is written as:CO

6. Naming
Aldehydes & Ketones

7. IUPAC Rules for Naming Aldehydes
To establish the parent name, select the longest continuous chain of carbon atoms that contains the aldehyde group.
The carbons of the parent chain are numbered starting with the aldehyde group. Since the aldehyde group is at the beginning (or end) of a chain, it is understood to be number 1.

8. IUPAC Rules for Naming Aldehydes
3. Form the parent aldehyde name by dropping the –e from the corresponding alkane name and adding the suffix –al.
4. Other groups attached to the parent chain are named and numbered as we have done before.

9. Naming Aldehydes
ethanal
4-methylhexanal

10. IUPAC Names of Several Aldehydes
Formula (condensed)
IUPAC Name
HCHO
Methanal
CH3CHO
Ethanal
CH3CH2CHO
Propanal
CH3CH2CH2CHO
Butanal
CH3CHCHO
2-Methyl propanal 
CH3

11. Common Names for Aldehydes
Acetic acid
Formic acid
Benzoic acid
[O]

12. IUPAC Rules for Naming Ketones
To establish the parent name, select the longest continuous chain of carbon atoms that contain the ketone group.
Form the parent name by dropping the –e from the corresponding alkane name and add the suffix –one.

13. IUPAC Rules for Naming Ketones
3. If the chain is longer than four carbons, it is numbered so that the carbonyl group has the smallest number possible; this number is prefixed to the parent name of the ketone.
4. Other groups attached to the parent chain are named and numbered as we have done before.

14. Naming Ketones
2-pentanone

15. Common Names for Ketones
dimethyl ketone

16. Bonding and Physical Properties

17. Bonding
The carbon atom of the carbonyl group is sp2-hybridized and is joined to three other atoms by sigma bonds.
The fourth bond is made by overlapping p electrons of carbon and oxygen to form a pi bond between the carbon and oxygen atoms.

18. Bonding
Because the oxygen atom is considerably more electronegative than carbon, the C=O group is polar.
Many of the chemical reactions of aldehydes and ketones are due to this polarity.

19. Properties
Unlike alcohols, aldehydes and ketones cannot hydrogen-bond to themselves, because no hydrogen atom is attached to the oxygen atom of the carbonyl group.
Aldehydes and ketones, therefore, have lower boiling points than alcohols of comparable molar mass.

20. Effect of Hydrogen Bonding on Physical Properties20 20

21. Boiling Points of Aldehydes, Ketones, and Corresponding Alcohols.
Name
Mole Weight
Boiling Point (°C)
1-Propanol 60 97
Propanal 58 49
Propanone 56
1-Butanol 74
118
Butanal 72 76
Butanone 80
1-Pentanol 88
138
Pentanal 86
103
2-Pentanone
102

22. Chemical Properties of Aldehydes & Ketones

23. Reactions of Aldehydes & Ketones
Oxidation
aldehydes only
Reduction
aldehydes and ketones
Addition

24. Oxidation of Aldehydes
Aldehydes are easily oxidized to carboxylic acids by a variety of oxidizing agents, including (under some conditions) oxygen of the air.

25. Tollens’ Silver Mirror Test
Tollens’ reagent,
which contains Ag+, oxidizes aldehydes, but not ketones.
Ag+ is reduced to metallic Ag, which appears as a “mirror” in the test tube.
Ag+ + e– → Ag(s) 25

27. Fehling and Benedict Tests
Benedict’s reagent, which contains Cu2+ ions in an alkaline medium, reacts with aldehydes that have an adjacent OH group.
an aldehyde is oxidized to a carboxylic acid, while Cu2+ is reduced to give brick red Cu2O(s). 27

28. green  orange  red  brown
Increasing amounts of reducing sugar
green  orange  red  brown

29. Tollens, Fehling & Benedict Tests
Because most ketones do not give a positive with Tollens, Fehling, or Benedict solutions, these tests are used to distinguish between aldehydes and ketones.

30. Biochemical Oxidation of Aldehydes
When our cells ‘burn’ carbohydrates, they take advantage of the aldehyde reactivity.
The aldehyde is oxidized to a carboxylic acid and is eventually converted to carbon dioxide, which is then exhaled.
This stepwise oxidation provides some of the energy necessary to sustain life.

31. Reduction of Aldehydes & Ketones
Aldehydes and ketones are easily reduced to alcohols using LiAlH4,
NaBH4 , or H2/Ni .
Aldehydes yield primary alcohols (1) while ketones yield secondary
alcohols ( 2) . 31 31

32. Addition Reactions of Aldehydes & Ketones
Common addition reactions:
Addition of alcohols
2,4-dinitrophenylhydrazine (2,4-DNP)

33. Addition of Alcohols
Aldehydes react with alcohols and a trace of acid to yield hemiacetals
as shown here. 33 33

34. Addition of Alcohols
In the presence of excess alcohol and a strong acid such as dry HCl,
aldehydes or hemiacetals react with a second molecule of the alcohol
to yield an acetal. 34 34

35. Intramolecular Addition of Alcohols
Cyclic hemiacetals or hemiketals can form when the alcohol and the carbonyl group exist within the same molecule . 35 35

36. Utility of the Hydroxyl Functional Group

37. 2,4-dinitrophenylhydrazine (2,4-DNP)

38. 2,4-dinitrophenylhydrazine (2,4-DNP)
The carbonyl carbon in both aldehydes and ketones reacts with 2,4-DNP to form heavy yellow to orange crystalline solids.
These solids were used extensively for identification purposes before the use of spectrometers.
The solid is purified by crystallization and its melting point compared to those of known structure.

43. Common Aldehydes & Ketones

44. Formaldehyde (Methanal)
Formaldehyde is made from methanol by reaction with oxygen (air) in the presence of a silver or copper catalyst.
2 CH3OH + O2  2H2C=O + 2H2O
Formaldehyde is widely used in the synthesis of polymers. Ag
heat

45. Acetaldehyde (Ethanal)
Its principal use is as an intermediate in the manufacture of other chemicals, such as acetic acid and 1-butanol.

46. Acetone and Methyl Ethyl Ketone
Acetone is used as a solvent in the manufacture of drugs, chemicals, and explosives. It is also used as a solvent.
Methyl ethyl ketone (MEK) is also widely used as a solvent, especially for lacquers.

47. Aldehydes & Ketones in Nature

53. Condensation Polymers

54. Leo Baekeland ( )

55. Phenol-Formaldehyde Polymers (Bakelite)
A phenolic is a condensation polymer made from phenol as shown here.
This is a section of a phenolic
( i.e. Bakelite) which is an example
of a thermosetting polymer. These
polymers are used in electrical
equipment because of their
insulating and fire-resistant properties. 55 55

56. Bakelite products

57. Bakelite products
GE Locomotive

59. The End

60. End of Chapter Learning Checks Try these after you have reviewed the chapter

61. Learning Check
Write the structure of butyl ethyl ketone. 61 61

62. Learning Check Answers
Write the structure of butyl ethyl ketone. 62 62

63. Learning Check
Give names for the following compounds. 63 63

64. Learning Check Answers
Give names for the following compounds. 64 64

65. Learning Check
Write the structure of cyclohexanone. 65 65

66. Learning Check Answers
Write the structure of cyclohexanone. 66 66

67. Learning Check
Rank these molecules based on boiling point from lowest to highest.
3-hexanol (molar mass = 102 g/mol)
3-hexanone (molar mass = 100 g/mol)
heptane (molar mass = 100 g/mol) 67 67

68. Learning Check Answers
Rank these molecules based on boiling point from lowest to highest.
3-hexanol (molar mass = 102 g/mol)
3-hexanone (molar mass = 100 g/mol)
heptane (molar mass = 100 g/mol) 68 68

69. Learning Check
Write the structures of the products, or indicate no reaction, for the following.
1. Propanone in the Tollens test
2. Pentanal in the Benedict’s test 69 69

70. Learning Check Answers
Write the structures of the products, or indicate no reaction, for the following.
1. Propanone in the Tollens test
2. Pentanal in the Benedict’s test 70 70

71. Learning Check The conversion of 2-pentanone to 2-pentanol is a(n):
Hydration
Dehydration
Hydrolysis
Oxidation
Reduction 71 71

72. Learning CheckAnswers
The conversion of 2-pentanone to 2-pentanol is a(n):
Hydration
Dehydration
Hydrolysis
Oxidation
Reduction
2-Pentanone is a ketone and 2-pentanol is an alcohol. The conversion of a ketone to an alcohol is a reduction. 72 72