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Chapter 23 Aldehydes and Ketones
Hein * Pattison * Arena * Best *
Version 1.0
Jerry Poteat
Science Department
Georgia Perimeter College
1 ©
John Wiley and Sons, Inc.
Chapter Outline
23.1 Structures of Aldehydes and Ketones
23.2 Naming Aldehydes and Ketones
23.3 Bonding and Physical Properties
23.4 Chemical Properties of Aldehydes and
Ketones
23.5 Common Aldehydes and Ketones
23.6 Condensation Polymers
23.1 Structures of Aldehydes and
Ketones
Aldehydes (i.e. RCHO) and ketones ( i.e. R2CO) are compounds with a
chemical structure that contain the characteristic carbonyl (C=O)
functional group as shown here.
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•The aldehyde group is often written as CHO.
For example,
•The ketone group is often written as CO.
For example,
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23.2 Naming Aldehydes and
Ketones
IUPAC Rules for Naming Aldehydes
1. Name the longest continuous carbon chain
containing the CHO group.
2. The CHO carbon is numbered carbon one
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IUPAC Rules for Naming Aldehydes
3. Drop an –e from the corresponding alkane parent
name and add the suffix –al.
4. Number and name groups attached to the chain as
we have done before.
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Examples of Naming Aldehydes
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Some aldehydes have common names as seen this table.
Benzaldehyde is a common
aromatic aldehyde.
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Dialdehydes
Dialdehydes are named by adding the suffix –dial to the
corresponding hydrocarbon name.
For example a molecule with four carbons and two aldehyde
groups would be named butanedial.
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IUPAC Rules for Naming Ketones
1. Name the longest continuous carbon chain
containing the C=O group.
2. Drop an –e from the corresponding alkane parent
name and add the suffix –one.
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IUPAC Rules for Naming Ketones
3. Carbon chains with four or more carbon atoms are numbered so the
carbonyl (C=O) carbon is given the lowest possible number and this
number is given as a prefix.
4. Attached groups are named and numbered as stated previously.
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Common Names of Ketones
Propanone and 2-butanone are widely available ketones and are
referred to by their common names as shown here.
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23.3 Bonding and Physical
Properties
Bonding
• The carbonyl (C=O) carbon is sp2-hybridized
with one pi (π) bond and three sigma(σ) bonds.
• The pi (π ) bond of the C=O group is reactive
and undergoes addition reactions.
• The C=O group is polarized which causes
aldehydes and ketones to be reactive.
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Effect of Hydrogen Bonding on Physical Properties
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Notice the alcohol in each group has the higher boiling
point due to hydrogen bonding.
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Figure 23.1 Naturally occurring aldehydes and ketones
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Figure 23.1(continued)
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23.4 Chemical Properties of
Aldehydes and Ketones
Reactions of Aldehydes & Ketones
The carbonyl functional group is the reactive site for aldehydes and
ketones. These compounds undergo the three broad classes of
reactions shown here. However aldehydes easily undergo oxidation
while ketones are much more difficult to oxidize.
Reaction Type
Aldehydes or Ketones
Oxidation
Aldehydes Only
Reduction
Both
Addition
Both
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Oxidation with Dichromate
Aldehydes (RCHO) are oxidized with dichromate to carboxylic acids
(RCOOH) as shown here.
Three well-known identification tests for RCHOs are based on the
fact that RCHOs are much easier to oxidize than R2COs. These tests
are Tollens, Fehling, and Benedict tests.
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Oxidation with Ag+ (Tollens test)
Aldehydes can be identified using the Tollens test ( i.e. the
silver-mirror test) as seen here .
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Oxidation with Cu 2+ ( Fehling and Benedict Tests)
The aldehyde group (RCHO) is oxidized to a carboxylic acid by Cu2+
ions in both the Fehling and Benedict tests. Both tests are carried out
in an alkaline solution. The tests are very similar except the Fehling test
uses tartaric acid to complex Cu2+ while the Benedict test uses citric acid.
Test
Positive Test Result for RCHO
Tollens
Silver mirror
Fehling
Blue → Brick-red
Benedict
Blue → Brick-red
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Ketones and the Tollens/Fehling/ Benedict Tests
All three tests are used to distinguish aldehydes from ketones.
All three tests give a positive test result for aldehydes and a
negative test result for ketones .
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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) .
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Reduction of Aldehydes & Ketones
These are specific examples of an aldehyde and a ketone being reduced
to a primary and secondary alcohol respectively.
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Applications in Biochemistry
Oxidation and reduction of RCHOs/R2COs is important in biochemistry.
For example pyruvic acid is reduced to lactic acid in muscle cells and
then lactic acid is oxidized back to pyruvic acid in the liver as shown
below.
This reaction sequence is important because the body uses this sequence
as an additional pathway to regenerate glucose.
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Addition Reactions of Aldehydes & Ketones
This table summarizes addition reactions of aldehydes
(RCHO) and ketones (R2CO)
Reactants
RCHO +
R2CO +
RCHO +
R2CO +
RCHO or
2RCHO
2R2CO
ROH
ROH
2ROH
2ROH
R2CO + HCN
Product
Hemiacetal
Hemiketal
Acetal
Ketal
Cyanohydrin
Aldol
- hydroxy ketone
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Hemiacetals, Hemiketals, Acetals, and Ketals
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Addition of Alcohols
Aldehydes react with alcohols and a trace of acid to yield hemiacetals
as shown here.
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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.
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Intramolecular Addition of Alcohols
Cyclic hemiacetals or hemiketals can form when the alcohol and
the carbonyl group exist within the same molecule .
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Addition of HCN
The addition of HCN to aldehydes and ketones yields cyanohydrins. A
cyanohydrin is a compound that has a cyano group(-CN) and a
hydroxyl group (-OH) on the same carbon as shown below.
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Synthetic Importance of Cyanohydrins
Hydrolysis of cyanohydrins yields an -hydroxy carboxylic acid.
Consequently cyanohydrins are important synthetic intermediates for
-hydroxy acids as well as amino acids.
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Aldol Condensation (Self-Addition)
An Aldol condensation is an
addition reaction between two
molecules of the same aldehyde
to yield a -hydroxyaldehyde
or a -hydroxyketone in the case of a
ketone.
The notations , , etc. refer to the
carbon atoms next to the carbonyl group
carbon as shown here. The -hydrogen is
a hydrogen atom attached to an -carbon
atom. -Hydrogen atoms are slightly
acidic and are more easily released than
, , or  H atoms during an aldol reaction.
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Mechanism of the Aldol Condensation
Note the transfer of the -hydrogen in step I and the addition of
the anion to the cation in step II.
Step I
Step II
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Mechanism of the Aldol Condensation
Ketones with -hydrogen atoms also undergo aldol reactions.
Aldol reactions occur
naturally in collagen
molecules that are layered
together as shown here.
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23.5 Common Aldehydes and
Ketones
23.6 Condensation Polymers
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Common Aldehydes & Ketones (23.5)
Formaldehyde and Acetaldehyde
Formaldehyde is used in manufacturing polymers, fumigation, and
preserving biological specimens. It is prepared over a copper or silver
catalyst.
Acetaldehyde is used as an intermediate in the manufacture of other
chemicals such as acetic acid.
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Acetone and Methyl Ethyl Ketone(MEK)
Acetone and MEK are widely used solvents used in industry and
research laboratories . For example acetone is found in fingernail
polish remover while MEK is found in lacquers.
Also, acetone is used as an indicator of diabetes because it a product of
lipid metabolism . Acetone and MEK are prepared by oxidizing alcohols.
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(23.6) Condensation Polymers
Condensation polymers are substances that produce a small
molecule like water during polymerization.
Polyesters, polyamides, polyurethanes, and phenolics
represent four important classes of condensation polymers.
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Preparation of a Condensation Polymer
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.
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Chapter 23 Summary
The properties of aldehydes and ketones are largely determined by
the polarized carbonyl group(
).
Both class of compounds have lower boiling points than alcohols
because hydrogen bonding is not possible in pure samples of these
substances.
Aldehydes undergo oxidation but ketones generally do not undergo
oxidation under the same conditions as aldehydes which leads to the
Tollens/Fehling/Benedict tests that are specific for differentiating
RCHOs from R2COs.
 Both class of compounds undergo reduction to alcohols with
reducing agents such as LiAlH4, NaBH4, and H2/Ni.
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Chapter 23 Summary

Both class of compounds undergo addition reactions:
(1)
yielding hemiacetals, hemiketals, acetals, and ketals when
reacted with alcohols,
(2)
yielding cyanohydrins when reacted with hydrogen cyanide
(HCN), and ….
(3)
yielding aldol products when undergoing self-addition.
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