Download Aldehydes, Ketones, & Chiral Molecules

Chapter 14 Aldehydes, Ketones,
and Chiral Molecules
14.1
Aldehydes and Ketones
Copyright © 2007 by Pearson Education, Inc.
Publishing as Benjamin Cummings
1
Carbonyl Group in Aldehydes and
Ketones
A carbonyl group
 In an aldehyde is
attached to at
least one H atom.
 In a ketone is
attached to two
carbon groups.
2
Naming Aldehydes
An aldehyde
 Has an IUPAC name in which the -e in the alkane
name is changed to -al.
 Has a common name for the first four aldehydes that
use the prefixes form (1C), acet (2C), propion (3C),
and butyr (4C), followed by aldehyde.
O
O
O
║
║
║
H−C−H
CH3−C−H
CH3−CH2−C−H
methanal
(formaldehyde)
ethanal
(acetaldehyde)
propanal
(propionaldehyde)
3
Naming Aldehydes
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Publishing as Benjamin Cummings
4
Aldehydes in Flavorings
 Several naturally occurring aldehydes are used
as flavorings for foods and fragrances.
O
H
C
Benzaldehyde
(almonds)
O
CH=CH C
H
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Publishing as Benjamin Cummings
Cinnamaldehyde (cinnamon)
5
Naming Ketones
Ketones are named
 In the IUPAC system by replacing the -e in the alkane
name with one. The carbonyl carbon is indicated by a
number.
 With a common name by indicating the alkyl groups
attached to the carbonyl group in alphabetical order
followed by ketone.
O
O
║
║
CH3−C−CH3
CH3−C−CH2−CH3
propanone
2-butanone
(dimethyl ketone)
(ethyl methyl ketone)
6
Ketones in Common Use
Butter
flavoring
Nail polish remover,
Solvent
Propanone,
Dimethylketone,
Acetone
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7
Learning Check
Classify each as 1) aldehyde or 2) ketone.
O
O
||
||
A. CH3—CH2—C—CH3
B. CH3—C—H
CH3
O
|
||
C. CH3—C—CH2—C—H
|
CH3
O
D.
8
Solution
A. 2) ketone
B. 1) aldehyde
C. 1) aldehyde
D. 2) ketone
9
Learning Check
Classify each as an aldehyde (1), ketone (2), alcohol (3),
or ether (4).
O
║
A. CH3─CH2─C─CH3
B. CH3─O─CH3
CH3
O
│
║
C. CH3─C─CH2─C─H
│
CH3
OH
│
D. CH3─CH─CH3
10
Solution
Classify each as an aldehyde (1), ketone (2),
alcohol (3), or ether (4).
O
║
A. CH3─CH2─C─CH3
B. CH3─O─CH3
(2) ketone
(4) ether
CH3
O
OH
│
║
│
C. CH3─C─CH2─C─H
D. CH3─CH─CH3
│
CH3
(1) aldehyde
(3) alcohol
11
Learning Check
Name each of the following:
O
║
1. CH3─CH2─CH2─CH2─C─H
O
║
2. Cl─CH2─CH2─C─H
O
║
3. CH3─CH2─C─CH3
12
Solution
O
║
1. CH3─CH2─CH2─CH2─C─H
pentanal
O
║
2. Cl─CH2─CH2─C─H
3-chloropropanal
O
║
3. CH3─CH2─C─CH3
2-butanone;
ethyl methyl ketone
13
Learning Check
Name the following compounds.
O
||
A. CH3—CH2—CH2—C—CH3
B.
O
CH3
O
|
||
C. CH3—C—CH2—C—H
|
CH3
14
Solution
A.
2-pentanone; methyl propyl ketone
B.
cyclohexanone
C,
3,3-dimethylbutanal
15
Learning Check
Draw the structural formulas for each:
A. 4-methylpentanal
B. 2,3-dichloropropanal
C. 3-methyl-2-butanone
16
Solution
A. 4-methylpentanal
CH3
O
│
║
CH3─CH─CH2─CH2─C─H
B. 2,3-dichloropropanal
Cl O
│
║
Cl─CH2─CH─C─H
C. 3-methyl-2-butanone
CH3 O
│
║
CH3─CH─C─CH3
17
Chapter 14 Aldehydes, Ketones,
and Chiral Molecules
14.2
Physical Properties
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18
Polar Carbonyl Group
The polar carbonyl group
 Provides dipole-dipole interactions.
+ + C=O
C=O
 Does not have H on the oxygen atom.
 Cannot form hydrogen bonds.
19
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.
20
Comparison of Boiling Points
58
Aldehydes and ketones have
 Higher boiling points than alkanes and ethers of
similar mass.
 Lower boiling points than alcohols of similar mass.
21
Learning Check
Select the compound in each pair that would have the
Higher boiling point.
A. CH3—CH2—CH3 or CH3—CH2—OH
O
B.
or
C. CH3—CH2—OH or CH3—O—CH3
22
Solution
A. CH3—CH2—OH
B.
O
C. CH3—CH2—OH
23
Solubility in Water
The electronegative O atom of the carbonyl
group in aldehydes and ketones forms
hydrogen bonds with water.
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24
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
25
Solution
A. CH3—CH2—CH3
insoluble
B. CH3—CH2—OH
soluble
O
||
C. CH3—CH2—CH2—C—H
soluble
O
||
D. CH3—C—CH3
soluble
26
Chapter 14 Aldehydes, Ketones and
Chiral Molecules
14.3
Oxidation and Reduction
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27
Oxidation
 Aldehydes are easily oxidized to carboxylic acids.
O
O
||
[O]
||
CH3—C—H
CH3—C—OH
Acetaldehyde
Acetic acid
28
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.
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29
Benedict’s Test
In the Benedict’s Test,
 Cu2+ reacts with aldehydes
that have an adjacent OH
group.
 Aldehydes are oxidized to
carboxylic acids.
 Cu2+ is reduced to give
Cu2O(s).
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Publishing as Benjamin Cummings
30
Learning Check
Write the structure and name of the oxidized product
when each is mixed with Tollens’ reagent.
1. butanal
2. acetaldehyde
3. ethyl methyl ketone
31
Solution
1. butanal
O
||
CH3—CH2—CH2—C—OH
butanoic acid
2. acetaldehyde
O
||
CH3—C—OH
acetic acid
3. ethyl methyl ketone None. Ketones are not
oxidized by Tollen’s reagent.
32
Chapter 14 Aldehydes, Ketones and
Chiral Molecules
14.4
Addition Reactions
| + + —C=O + X—Y
|
—C—O—X
|
Y
33
Addition Reactions
When a polar molecule adds to the carbonyl group of
an aldehyde or ketone
 The negative part of the added molecule bonds to the
positive carbonyl carbon.
 The positive part of the added molecule bonds to the
negative carbonyl oxygen.
| + + —C=O + X—Y
|
— C—O—X
|
Y
34
Acetal Formation
 Alcohols add to the carbonyl group of aldehydes and
ketones.
 The addition of two alcohols forms acetals.
Copyright © 2007 by Pearson Education, Inc. Publishing as Benjamin Cummings
35
Hemiacetal Formation
 The addition of one alcohol to an aldehyde or ketone
forms an intermediate called a hemiacetal.
 Usually, hemiacetals are unstable and difficult to
isolate.
Copyright © 2007 by Pearson Education, Inc. Publishing as Benjamin Cummings
36
Cyclic Hemiacetals
A stable cyclic hemiacetal forms when the C=O
group and the —OH are both part of a five- or
six-atom carbon compound.
Copyright © 2007 by Pearson Education, Inc. Publishing as Benjamin Cummings
37
Learning Check
Identify each as a 1) hemiacetal or 2) acetal.
O—CH3
|
A. CH3—CH2—C—H
|
OH
O—CH2CH3
|
B. CH3—CH2—C—CH2—CH3
|
O—CH2CH3
38
Solution
O—CH3
|
A. CH3—CH2—C—H
|
OH
1) hemiacetal
O—CH2CH3
|
B. CH3—CH2—C—CH2—CH3
|
O—CH2CH3
2) acetal
39
Learning Check
Draw the structure of the acetal formed by adding
CH3OH to butanal.
40
Solution
Draw the structure of the acetal formed by adding
CH3OH to butanal.
O—CH3
|
CH3—CH2—CH2—C—H
|
O—CH3
41
Chapter 14 Aldehydes, Ketones,
and Chiral Molecules
15.5
Chiral Molecules
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Publishing as Benjamin Cummings
42
Chiral Compounds
Chiral compounds
 Have the same number of atoms
arranged differently in space.
 Have one or more chiral carbon
atoms bonded to four different
groups.
 Are mirror images like your
hands. Try to superimpose your
thumbs, palms, back of hands,
and little fingers.
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43
Mirror Images
The mirror images of
 Chiral compounds cannot be superimposed.
 Two compounds of bromochloroiodomethane can align
the H and I atoms, which places the Cl and Br atoms
on opposite sides.
Copyright © 2007 by Pearson Education, Inc Publishing as Benjamin Cummings
44
Achiral Structures are
Superimposable
 When the mirror image of an achiral structure is
rotated, the structure can be aligned with the initial
structure. Thus this mirror image is superimposable.
Copyright © 2007 by Pearson Education, Inc Publishing as Benjamin Cummings
45
Some Everyday Chiral and
Achiral Objects
46
Enantiomers
Have same
 mp,
 bp,
 same chemistry
 Except: reaction with other chiral molecules
47
Smell:
R-(-)-carvone
Spearmint
S-(+)-carvone
Caraway
(Dill)
(Manderine Orange Peel)
48
Enantiomers




Have same
mp,
bp,
same chemistry
 Except: reaction with other chiral molecules
•Except: rotation of plane of polarized light
49
Learning Check
Identify each as a chiral or achiral compound.
Cl
Cl
H
C
CH3
CH2CH3
A
H
C
Cl
CH3
H
C
H
Br
B
C
CH3
50
Solution
Identify each as a chiral or achiral compound.
Cl
Cl
H
C
CH3
H
C
Cl
CH3
H
C
H
Br
A
B
C
chiral
achiral
CH2CH3
CH3
chiral
51
Fischer Projections
A Fischer projection
 Is a 2-dimensional representation of a 3-dimensional
molecule.
 Places the most oxidized group at the top.
 Uses vertical lines in place of dashes for bonds that
go back.
 Uses horizontal lines in place of wedges for bonds
that come forward.
52
Drawing Fischer Projections
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53
D and L Notations
 By convention, the letter L is assigned to the structure
with the —OH on the left.
 The letter D is assigned to the structure with the —OH
on the right.
Copyright © 2007 by Pearson Education, Inc Publishing as Benjamin Cummings
54
Learning Check
Indicate whether each pair is a mirror image that
cannot be superimposed.
CH2OH
CH2OH
A.
B.
H
H
C
CH3
and
CH3 C
Br
Br
Cl
Cl
C
H
CH3
and
CH3 C
H
H
H
55
Solution
Indicate whether each pair is a mirror image that
cannot be superimposed
CH2OH
A.
B.
H
H
C
CH3
CH2OH
and
CH3 C
Br
Br
Cl
Cl
C
H
CH3
and
CH3 C
Yes
H
No
H
H
56