Chapter 13 Organic Compounds
with oxygen and Sulfur
13.5
Properties of Aldehydes and Ketones
1
Physical Properties
• The polar carbonyl group provides dipole-dipole
interactions.
+ -
C=O
+ -
C=O
• Without an H on the oxygen, aldehydes and
ketones cannot form hydrogen bonds.
2
Boiling Points
Aldehydes and ketones have
• polar carbonyl groups (C=O).
+ -
C=O
• attractions between polar groups.
+ -
+ -
C=O
C=O
• higher boiling points than alkanes and ethers of
similar mass.
• lower boiling points than alcohols of similar mass.
3
Comparison of Boiling Points
58
4
Solubility in Water
The electronegative O atom of the carbonyl group of
aldehydes and ketones forms hydrogen bonds with water.
5
Learning Check
Indicate if each is soluble or insoluble in water.
A. CH3—CH2—CH3
B. CH3—CH2—OH
O
||
C. CH3—CH2—CH2—C—H
O
||
D. CH3—C—CH3
6
Solution
Indicate if each is soluble or insoluble in water.
A. CH3—CH2—CH3
insoluble
B. CH3—CH2—OH
soluble
O
||
C. CH3—CH2—CH2—C—H
soluble
O
||
D. CH3—C—CH3
soluble
7
Tollens’ Test
In Tollens’ 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.
8
Benedict’s Test
In the Benedict’s test,
• Benedict’s reagent,
which contains Cu2+,
reacts with aldehydes
that have an adjacent
OH group.
• An aldehyde is oxidized
to a carboxylic acid,
while Cu2+ is reduced to
give red Cu2O(s).
9
Learning Check
Write the structure and name of the oxidized product
when each is mixed with Tollens’ reagent.
A. butanal
B. acetaldehyde
C. ethyl methyl ketone
10
Solution
A. butanal
O
||
CH3—CH2—CH2—C—OH
butanoic acid
B. acetaldehyde
O
||
CH3—C—OH
acetic acid
C. ethyl methyl ketone
None.
Ketones are not oxidized by Tollen’s reagent.
11