Download 14_Aldehydes_and_Ketones

General, Organic, and
Biological Chemistry
Fourth Edition
Karen Timberlake
Chapter 14
Aldehydes, Ketones,
and Chiral Molecules
14.1
Aldehydes and Ketones
Lectures
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Aldehydes and Ketones
A carbonyl group,
 in an aldehyde, has a
carbonyl carbon bonded
to one H atom.
 in a ketone, has the
carbonyl carbon bonded
to two carbon groups.
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Chapter 14, Section 1
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.
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Chapter 14, Section 1
3
Guide to Naming Aldehydes
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Chapter 14, Section 1
4
Aldehydes in Flavorings
 Several naturally occurring aldehydes are used
as flavorings for foods and fragrances.
O
C
H
Benzaldehyde
(almonds)
O
CH=CH C
H
Cinnamaldehyde (cinnamon)
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Chapter 14, Section 1
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 carbon in alphabetical order
followed by ketone.
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Chapter 14, Section 1
6
Guide to Naming Ketones
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Chapter 14, Section 1
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Learning Check
Give the IUPAC name for the following ketone.
H2
C
O
H3 C
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Chapter 14, Section 1
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Solution
Give the IUPAC name for the following ketone.
H2
C
O
H3 C
Step 1 Name the longest carbon chain by
replacing the -e in the alkane name
with -one.
cyclopentanone
H2
C
O
H3 C
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Chapter 14, Section 1
9
Solution
Give the IUPAC name for the following ketone.
H2
C
O
H3 C
Step 2 Number the carbon chain from the end
nearer the carbonyl group, and indicate
its location.
1-cyclopentanone
H2
2
C
H3 C
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Chapter 14, Section 1
O
3
1
10
Solution
Give the IUPAC name for the following ketone.
H2
C
O
H3 C
Step 3 Name and number any substituents on
the carbon chain.
3-ethyl-1-cyclopentanone
H2
C
H3 C
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Chapter 14, Section 1
2
O
3
1
11
Boiling Points
Aldehydes and ketones have
 dipole–dipole interactions between polar groups.
 higher boiling points than alkanes and ethers of
similar mass due to dipole–dipole interactions.
 lower boiling points than alcohols of similar mass
because they do not form hydrogen bonds.
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Chapter 14, Section 1
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Comparison of Boiling Points
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Chapter 14, Section 1
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Solubility of Aldehydes and
Ketones in Water
Aldehydes and ketones
 with one to four carbons are soluble in water.
 with five or more carbons are not very soluble in
water.
 form hydrogen bonds with water between the
carbonyl oxygen and hydrogen atoms of water.
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Chapter 14, Section 1
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Reduction of Aldehydes, Ketones
Aldehydes and ketones are reduced by hydrogen (H2)
with a catalyst or sodium borohydride (NaBH4), thus
 decreasing the number of carbon-oxygen bonds,
 reducing aldehydes to primary alcohols, and
 reducing ketones to secondary alcohols.
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Chapter 14, Section 1
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Acetals and Hemiacetals
Hemiacetals
 are carbon atoms that contain a hydroxyl group –OH
and an alkoxy group –OR.
 are formed when an alcohol adds to an aldehyde or
ketone in the presence of an acid catalyst.
 react with a second alcohol molecule to produce an
acetal, a carbon with two alkoxy groups –OR.
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Chapter 14, Section 1
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Acetals from Aldehydes
Alcohol adds to the aldehyde carbonyl producing a
hemiacetal. When a second alcohol adds, it
forms an acetal.
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Chapter 14, Section 1
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Acetals from Ketones
Ketones
 are less reactive than aldehydes because the
carbonyl carbon is more positive in aldehydes.
 react with one alcohol molecule to form a hemiacetal,
and react with a second alcohol molecule to form an
acetal.
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Chapter 14, Section 1
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Stereoisomers
Structural Isomers
have the same formula
but different bonding
arrangements.
Stereoisomers have
atoms that are bonded
in the same sequence,
but differ in the way
they are arranged in
space.
Stereoisomers are
molecules that are
nonsuperimposable
mirror images.
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Chapter 14, Section 1
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Chirality
 Molecules are chiral when their mirror images cannot
be completely matched. They are said to be
nonsuperimposable.
 Your hands are chiral. Try to superimpose your
thumbs, palms, back of hands, and little fingers.
 When the mirror image of an object is identical and
can be superimposed on the original, it is achiral.
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Chapter 14, Section 1
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Hands Are Like Chiral Objects
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Chapter 14, Section 1
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Chiral or Achiral
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Chapter 14, Section 1
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Chiral Carbon Atoms
Carbon atoms are chiral if
 they have 4 different atoms or groups.
 they have mirror images like your hands.
When stereoisomers cannot be superimposed, they are
called enantiomers.
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Chapter 14, Section 1
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Mirror Images
The mirror images of bromochloroiodomethane can align
the H and I atoms, which places the Cl and Br atoms on
opposite sides.
(a) The enantiomers of a chiral molecule are mirror images.
(b) The enantiomers of a chiral molecule cannot be superimposed on
. each other.
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Chapter 14, Section 1
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Achiral Structures Are
Superimposable
When the mirror image of an achiral structure is rotated,
 the structure is aligned with its initial structure.
 its mirror image is superimposable.
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Biological Effects of Stereoisomers
Molecules in nature also have mirror images, and often
one stereoisomer has a different biological effect than
the other one.
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Chapter 14, Section 1
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Learning Check
Identify each as a chiral or achiral compound.
A.
B.
Cl
H C CH3
CH2 CH3
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C.
Cl
H C CH3
Br
Chapter 14, Section 1
Cl
H C CH3
H
27
Solution
Identify each as a chiral or achiral compound.
A.
B.
Cl
H C CH3
CH2 CH3
chiral
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C.
Cl
H C CH3
Cl
H C CH3
Br
H
chiral
antichiral
Chapter 14, Section 1
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Fischer Projections
A Fischer projection
 is a two-dimensional representation of a
molecule.
 places the most oxidized group at the top.
 uses vertical lines for bonds that go back.
 uses horizontal lines for bonds that go forward.
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Chapter 14, Section 1
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Drawing Fischer Projections
For compounds with two or more chiral carbons, the
designation as a D or L isomer is determined by the
position of the –OH group attached to the chiral carbon
farthest from the carbonyl group.
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Chapter 14, Section 1
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Learning Check
Indicate whether each of the following pairs of Fischer
projections can or cannot be superimposed.
CH2 OH
A.
B.
H
CH3
and
H3C
H
Br
Br
H
H
H
CH3
Br
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CH2 OH
and
H3C
H
Br
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Solution
Indicate whether each of the following pairs of Fischer
projections can or cannot be superimposed:
CH2 OH
A.
B.
H
CH3
and
H3C
Br
Br
H
H
H
CH3
Br
© 2013 Pearson Education, Inc.
CH2 OH
and
H3C
H
cannot be
superimposed
H
can be
superimposed
Br
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Learning Check
Identify the following as a D or L isomer.
CHO
H
OH
HO
H
HO
H
H
OH
CH2OH
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Chapter 14, Section 1
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Solution
Identify the following as a D or L isomer.
CHO
H
OH
HO
H
HO
H
H
OH
The –OH group is
on the right,
it is a D isomer.
CH2OH
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