Chapter 5 Aldehydes and Ketones

Chapter 5
Aldehydes and Ketones
General, Organic, and Biological Chemistry,Fifth Edition
H. Stephen Stoker
Brroks/Cole Cengage Learning. Permission required for reproduction or display.
Prepared by:
GIZEL R. SANTIAGO

3
Chapter 3 Topics
• The Carbonyl Group
• Compounds Containing a Carbonyl Group
• The Aldehyde and Ketone Functional Groups
• Nomenclature for Aldehydes
• Nomenclature for Ketones
• Isomerism for Aldehydes and Ketones
• Selected Common Aldehydes and Ketones
• Physical Properties of Aldehydes and Ketones
• Preparation of Aldehydes and Ketones
• Oxidation and Reduction of Aldehydes and Ketones
• Reaction of Aldehydes and Ketones with Alcohols

4
The Carbonyl Group
Both aldehydes and ketones contain a
carbonyl functional group. A carbonyl group
is a carbon atom double-bonded to an
oxygen atom. The structural representation
for a carbonyl group is

5
The Carbonyl Group
Carbon–oxygen and carbon–carbon double bonds
differ in a major way. A carbon– oxygen double
bond is polar, and a carbon–carbon double bond is
nonpolar. The electronegativity of oxygen (3.5) is
much greater than that of carbon (2.5). Hence the
carbon–oxygen double bond is polarized, the
oxygen atom acquiring a fractional negative
charge (-) and the carbon atom acquiring a
fractional positive charge (+).

7
The Carbonyl Group
All carbonyl groups have a trigonal planar structure.
The bond angles between the three atoms attached
to the carbonyl carbon atom are 1200, as would be
predicted using VSEPR theory.

8
Compounds Containing A Carbonyl Group
The carbon atom of a carbonyl group must
form two other bonds in addition to the
carbon–oxygen double bond in order to
have four bonds. The nature of these two
additional bonds determines the type of
carbonyl-containing compound it is.

9
1. Aldehydes. In an aldehyde, one of the two
additional bonds that the carbonyl carbon
atom forms must be to hydrogen atom. The
other may be to a hydrogen atom, an alkyl or
cycloalkyl group, or an aromatic ring system.

10
2. Ketones. In a ketone, both of the additional
bonds of the carbonyl carbon atom must be to
another carbon atom that is part of an alkyl,
cycloalkyl, or aromatic group.

11
3. Carboxylic acids. In a carboxylic acid, one of the
two additional bonds of the carbonyl carbon atom
must be to a hydroxyl group, and the other may be
to a hydrogen atom, an alkyl or cycloalkyl group, or
an aromatic ring system. The structural parameters
for a carboxylic acid are the same as those for an
aldehyde except that the mandatory hydroxyl group
replaces the mandatory hydrogen atom of an
aldehyde.

12

13
4. Esters. In an ester, one of the two additional
bonds of the carbonyl carbon atom must be to an
oxygen atom, which in turn is bonded to an alkyl,
cycloalkyl, or aromatic group. The other bond may
be to a hydrogen atom, alkyl or cycloalkyl group,
or an aromatic ring system. The structural
parameters for an ester differ from those for a
carboxylic acid only in that an —OH group has
become an —O—R or —O—Ar group.

14

15
5. Amides. The previous four types of
carbonyl compounds contain the elements
carbon, hydrogen, and oxygen. Amides are
different from these compounds in that the
element nitrogen, in addition to carbon,
hydrogen, and oxygen, is present. In an
amide, an amino group (—NH2) or
substituted amino group replaces the —OH
group of a carboxylic acid.

16

17
Aldehydes and ketones are the ﬁrst two of
the ﬁve major classes of carbonyl
compounds. They share the common
feature of having only one oxygen atom
present, the oxygen atom of the carbonyl
group.

18
The Aldehyde and Ketone Functional
Group
An aldehyde is a carbonyl-containing organic
compound in which the carbonyl carbon atom
has at least one hydrogen atom directly
attached to it. The remaining group attached
to the carbonyl carbon atom can be
hydrogen, an alkyl group (R), a cycloalkyl
group, or an aryl group (Ar).

19
Group
Linear notations for an
aldehyde functional group and
for an aldehyde itself are —
CHO and RCHO, respectively.
Note that the ordering of the
symbols H and O in these
notations is HO, not OH (which
denotes a hydroxyl group).

20
Group
A ketone is a carbonyl-
containing organic compound
in which the carbonyl carbon
atom has two other carbon
atoms directly attached to it.
The groups containing these
bonded carbon atoms may be
alkyl, cycloalkyl, or aryl.

21
Group
The general condensed
formula for a ketone is
RCOR, in which the oxygen
atom is understood to be
double-bonded to the
carbonyl carbon at the left
of it in the formula.

22
Group

23
Group
Cyclic aldehydes are not possible. For an
aldehyde carbonyl carbon atom to be
part of a ring system it would have to
form two bonds to ring atoms, which
would give it ﬁve bonds. Unlike
aldehydes, ketones can form cyclic
structures.

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Group

25
Group
Cyclic ketones are not heterocyclic ring
systems as were cyclic ethers.

26
Group
Aldehydes and ketones are related to alcohols in
the same manner that alkenes are related to
alkanes. Removal of hydrogen atoms from each of
two adjacent carbon atoms in an alkane produces
an alkene. In a like manner, removal of a hydrogen
atom from the —OH group of an alcohol and from
the carbon atom to which the hydroxyl group is
attached produces a carbonyl group.

27
Nomenclature for Aldehydes
Rule 1: Select as the parent carbon chain
the longest chain that includes the carbon
atom of the carbonyl group.
Rule 2: Name the parent chain by
changing the -e ending of the
corresponding alkane name to -al.

28
Rule 3: Number the parent chain by
assigning the number 1 to the carbonyl
carbon atom of the aldehyde group.
Rule 4: Determine the identity and
location of any substituents, and append
this information to the front of the parent
chain name.

31
Unlike the common names for alcohols and
ethers, the common names for aldehydes are
one word rather than two or three. In the
IUPAC system, aromatic aldehydes—
compounds in which an aldehyde group is
attached to a benzene ring—are named as
derivatives of benzaldehyde, the parent
compound.

32
The last of these compounds is named as a benzaldehyde
rather than as a phenol because the aldehyde group has
priority over the hydroxyl group in the IUPAC naming
system.

33
Nomenclature for Ketones
Assigning IUPAC names to ketones is similar to
naming aldehydes except that the ending -one is
used instead of -al.
Rule 1: S elect as the parent carbon chain the
longest carbon chain that includes the carbon
atom of the carbonyl group.
Rule 2: Name the parent chain by changing the -e
ending of the corresponding alkane name to -one.
This ending, -one, is pronounced "own."

34
Rule 3: Number the carbon chain such that the
carbonyl carbon atom receives the lowest possible
number. The position of the carbonyl carbon atom
is noted by placing a number immediately before
the name of the parent chain.
Rule 4: Determine the identity and location of any
substituents, and append this information to the
front of the parent chain name.

35
Rule 5: Cyclic ketones are named by assigning
the number 1 to the carbon atom of the
carbonyl group. The ring is then numbered to
give the lowest number(s) to the atom(s)
bearing substituents.

38
The procedure for coining common names for
ketones is the same as that used for ether
common names. They are constructed by giving,
in alphabetical order, the names of the alkyl or
aryl groups attached to the carbonyl functional
group and then adding the word ketone. Unlike
aldehyde common names, which are one word,
those for ketones are two or three words.

40
Three ketones have additional common
names besides those obtained with the
preceding procedures. These three ketones
are
Acetophenone is the simplest aromatic ketone.

41
Isomerism for Aldehydes and Ketones
Constitutional isomers exist for aldehydes and
for ketones, and between aldehydes and
ketones (functional group isomerism). The
compounds butanal and 2-methylpropanal
are examples of skeletal aldehyde isomers;
the compounds 2-pentanone and 3-
pentanone are examples of positional ketone
isomers.

42
Aldehydes and ketones with the same
number of carbon atoms and the same
degree of saturation are functional group
isomers. Molecular models for the
isomeric C3 compounds propanal and
propanone, which both have the
molecular formula C3H6O.

43

44

45

46

47
Selected Common Aldehydes and Ketones
Formaldehyde, the simplest aldehyde, with
only one carbon atom, is manufactured on a
large scale by the oxidation of methanol.

48
Its major use is in the manufacture of polymers. At room
temperature and pressure, formaldehyde is an irritating
gas. Bubbling this gas through water produces formalin,
an aqueous solution containing 37% formaldehyde by
mass or 40% by volume. (This represents the solubility
limit of formaldehyde gas in water.) Very little free
formaldehyde gas is actually present in formalin; most
of it reacts with water, producing methylene glycol.

49
Formalin is used for preserving biological specimens, anyone
who has experience in a biology laboratory is familiar with the
pungent odor of formalin. Formalin is also the most widely used
preservative chemical in embalming ﬂ uids used by morticians.
Its mode of action involves reaction with protein molecules in a
manner that links the protein molecules together; the result is a
“hardening” of the protein.

50
Acetone, a colorless, volatile liquid with a pleasant, mildly
“sweet” odor, is the simplest ketone and is also the ketone
used in largest volume in industry. Acetone is an excellent
solvent because it is miscible with both water and nonpolar
solvents. Acetone is the main ingredient in gasoline
treatments that are designed to solubilize water in the gas
tank and allow it to pass through the engine in miscible
form. Acetone can also be used to remove water from
glassware in the laboratory. And it is a major component of
some nail polish removers.

51
Small amounts of acetone are produced in the
human body in reactions related to obtaining
energy from fats. Normally, such acetone is
degraded to CO2 and H2O. Diabetic people
produce larger amounts of acetone, not all of
which can be degraded. The presence of acetone
in urine is a sign of diabetes. In severe diabetes,
the odor of acetone can be detected on the
person’s breath.

52

53
Naturally Occurring Aldehydes and Ketones
Aldehydes and ketones occur widely in nature.
Naturally occurring compounds of these types,
with higher molecular masses, usually have
pleasant odors and ﬂavors and are often used
for these properties in consumer products
(perfumes, air fresheners, and the like). The
unmistakable odor of melted butter is largely
due to the four-carbon diketone butanedione.

54
Naturally Occurring Aldehydes and Ketones
Many important steroid hormones are ketones,
including testosterone, the hormone that
controls the development of male sex
characteristics; progesterone, the hormone
secreted at the time of ovulation in females;
and cortisone, a hormone from the adrenal
glands that is used medicinally to relieve
inﬂammation.

56
Physical Properties of Aldehydes and
KetonesThe C1 and C2 aldehydes are gases at room
temperature. The C3 through C11 straight-chain
saturated aldehydes are liquids, and the higher
aldehydes are solids. The presence of alkyl groups
tends to lower both boiling points and melting
points, as does the presence of unsaturation in the
carbon chain. Lower-molecular-mass ketones are
colorless liquids at room temperature.

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Ketones

58
KetonesThe boiling points of aldehydes and ketones
are intermediate between those of alcohols
and alkanes of similar molecular mass.
Aldehydes and ketones have higher boiling
points than alkanes because of dipole–dipole
attractions between molecules. Carbonyl
group polarity makes these dipole–dipole
interactions possible.

59
KetonesThe boiling points of aldehydes and ketones
are intermediate between those of alcohols
and alkanes of similar molecular mass.
Aldehydes and ketones have higher boiling
points than alkanes because of dipole–dipole
attractions between molecules. Carbonyl
group polarity makes these dipole–dipole
interactions possible.

60
Ketones

61
Ketones

62
Ketones
Aldehydes and ketones have lower boiling
points than the corresponding alcohols
because no hydrogen bonding occurs as it
does with alcohols. Dipole–dipole
attractions are weaker forces than
hydrogen bonds.

63
KetonesWater molecules can hydrogen-bond with
aldehyde and ketone molecules. This
hydrogen bonding causes low-molecular-
mass aldehydes and ketones to be water
soluble. As the hydrocarbon portions get
larger, the water solubility of aldehydes and
ketones decreases.

64
KetonesAlthough low-molecular-mass aldehydes have
pungent, penetrating, unpleasant odors,
higher-molecular-mass aldehydes (above C8)
are more fragrant, especially benzaldehyde
derivatives. Ketones generally have pleasant
odors, and several are used in perfumes and
air fresheners.

65
Preparation of Aldehydes and
KetonesAldehydes and ketones can be
produced by the oxidation of
primary and secondary alcohols,
respectively, using mild oxidizing
agents such as KMnO4 or
K2Cr2O7.

66
Ketones

67
Ketones

68
Ketones

69
Ketones

70
Oxidation and Reduction Aldehydes
and KetonesAldehydes readily undergo oxidation to
carboxylic acids, and ketones are resistant to
oxidation.

71
and KetonesIn aldehyde oxidation, the aldehyde gains an oxygen
atom (supplied by the oxidizing agent). An increase
in the number of C—O bonds is one of the
operational deﬁnitions for the process of oxidation.
Oxidation of an aldehyde involves breaking a
carbon–hydrogen bond, and oxidation of a ketone
involves breaking a carbon–carbon bond.

72
and KetonesSeveral tests, based on the ease with which
aldehydes are oxidized, have been developed for
distinguishing between aldehydes and ketones, for
detecting the presence of aldehyde groups in sugars
(carbohydrates), and for measuring the amounts of
sugars present in a solution. The most widely used
of these tests are the Tollens test and Benedict’s
test.

73
and KetonesThe Tollens test, also called the silver mirror test,
involves a solution that contains silver nitrate
(AgNO3) and ammonia (NH3) in water. When
Tollens solution is added to an aldehyde, Ag+ ion
(the oxidizing agent) is reduced to silver metal,
which deposits on the inside of the test tube,
forming a silver mirror. The appearance of this
silver mirror is a positive test for the presence of
the aldehyde group.

74
and Ketones
The Ag+ ion will not oxidize ketones.

75
and KetonesBenedict’s test is similar to the Tollens test in that a
metal ion is the oxidizing agent. With this test, Cu2+
ion is reduced to Cu+ ion, which precipitates from
solution as Cu2O . Benedict’s solution is made by
dissolving copper sulfate, sodium citrate, and
sodium carbonate in water.

76
Reduction of Aldehydes and
KetonesAldehydes and ketones are easily reduced by hydrogen
gas (H2), in the presence of a catalyst (Ni, Pt, or Cu), to
form alcohols. The reduction of aldehydes produces
primary alcohols, and the reduction of ketones yields
secondary alcohols.

77
Ketones

78
KetonesIt is the addition of hydrogen atoms to the
carbon–oxygen double bond that produces the
alcohol in each of these reactions.

79
KetonesThis hydrogen addition process is very similar
to the addition of hydrogen to the carbon–
carbon double bond of an alkene to produce
an alkane.

80
KetonesAldehyde reduction and ketone reduction to
produce alcohols are the “opposite” of the
oxidation of alcohols to produce aldehydes
and ketones.

81
Reaction of Aldehydes and Ketones
with Alcohols
Aldehydes and ketones react with alcohols
to form hemiacetals and acetals. Reaction
with one molecule of alcohol produces a
hemiacetal, which is then converted to an
acetal by reaction with a second alcohol
molecule.

82
Reaction of Aldehydes and Ketones
with Alcohols
The Greek preﬁx hemi- means “half.” When
one alcohol molecule has reacted with the
aldehyde or ketone, the compound is halfway
to the ﬁnal acetal.

83
Hemiacetal Formation
Hemiacetal formation is an addition
reaction in which a molecule of alcohol
adds to the carbonyl group of an aldehyde
or ketone. The H portion of the alcohol
adds to the carbonyl oxygen atom, and the
R—O portion of the alcohol adds to the
carbonyl carbon atom.

85
Formally deﬁned, a hemiacetal is an organic
compound in which a carbon atom is bonded
to both a hydroxyl group (OOH) and an alkoxy
group (OOR). The functional group for a
hemiacetal is thus

86
The carbon atom of the hemiacetal functional
group is often referred to as the hemiacetal carbon
atom; it was the carbonyl carbon atom of the
aldehyde or ketone that reacted.
A reaction mixture containing a hemiacetal is
always in equilibrium with the alcohol and carbonyl
compound from which it was made, and the
equilibrium lies to the carbonyl compound side of
the reaction.

91
Acetal Formation
If a small amount of acid catalyst is added to a
hemiacetal reaction mixture, the hemiacetal
reacts with a second alcohol molecule, in a
condensation reaction, to form an acetal.

92
Acetal Formation
An acetal is an organic compound in which a
carbon atom is bonded to two alkoxy groups
(—OR). The functional group for an acetal is
thus

93
Acetal Formation
A speciﬁc example of acetal formation from a
hemiacetal is

94
Acetal Formation
Note that acetal formation does not involve
addition to a carbon–oxygen double bond as
hemiacetal formation does; no double bond is
present in either of the reactants involved in
acetal formation. Acetal formation involves a
substitution reaction; the —OR group of the
alcohol replaces the —OH group on the
hemiacetal.

95
Acetal Hydrolysis
A hydrolysis reaction is the reaction of a
compound with H2O, in which the compound
splits into two or more fragments as the
elements of water (H— and —OH) are added
to the compound. The products of acetal
hydrolysis are the aldehyde or ketone and
alcohols that originally reacted to form the
acetal.

98
Acetal Hydrolysis
The carbonyl hydrolysis product is an aldehyde if
the acetal carbon atom has a hydrogen atom
attached directly to it, and it is a ketone if no
hydrogen attachment is present.

100
Nomenclature for Hemiacetals and Acetals
A “descriptive” type of common nomenclature that
includes the terms hemiacetal and acetal as well as the
name of the carbonyl compound (aldehyde or ketone)
produced in the hydrolysis of the hemiacetal or acetal is
commonly used in describing such compounds. Two
examples of such nomenclature are

103
Formaldehyde-Based Polymer
Formaldehyde, the simplest aldehyde, is a proliﬁc
“polymer former.” As representative of its polymer
reactions, let us consider the reaction between
formaldehyde and phenol, under acidic conditions,
to form a phenol–formaldehyde network polymer.
A network polymer is a polymer in which
monomers are connected in a three-dimensional
cross-linked network.

104
When excess formaldehyde is present, the
polymerization proceeds via mono-, di-, and
trisubstituted phenols that are formed as
intermediates in the reaction between phenol and
formaldehyde.

105
The substituted phenols then interact
with each other by splitting out water
molecules. The ﬁ nal product is a complex,
large, three-dimensional network polymer
in which monomer units are linked via
methylene (—CH2—) bridges.

106

107
The ﬁrst synthetic plastic, Bakelite, produced
in 1907, was a phenol–formaldehyde polymer.
Early uses of Bakelite were in the
manufacture of billiard balls and “plastic”
jewelry. Modern phenol–formaldehyde
polymers, called phenolics, are adhesives
used in the production of plywood and
particle board.

108
Sulfur-Containing Carbonyl Group
The introduction of sulfur into a carbonyl group
produces two different classes of compounds
depending on whether the sulfur atom replaces
the carbonyl oxygen atom or the carbonyl carbon
atom.
Replacement of the carbonyl oxygen atom with
sulfur produces thiocarbonyl compounds—
thioaldehydes (thials) and thioketones (thiones)—
the simplest of which are

109
Thiocarbonyl compounds such as these are
unstable and readily decompose.

110
Replacement of the carbonyl carbon atom with
sulfur produces sulfoxides, compounds that are
much more stable than thiocarbonyl compounds.
The oxidation of a thioether (sulﬁde) constitutes the
most common route to a sulfoxide.

111
A highly interesting sulfoxide is DMSO
(dimethyl sulfoxide), a sulfur analog of
acetone, the simplest ketone.

112
DMSO is an odorless liquid with unusual
properties. Because of the presence of the
polar sulfur–oxide bond, DMSO is miscible
with water and also quite soluble in less polar
organic solvents. When rubbed on the skin,
DMSO has remarkable penetrating power
and is quickly absorbed into the body, where
it relieves pain and inﬂ ammation.

113
For many years it has been heralded as a “miracle drug” for
arthritis, sprains, burns, herpes, infections, and high blood
pressure. However, the FDA has steadfastly refused to
approve it for general medical use. For example, the FDA
says that DMSO’s powerful penetrating action could cause
an insecticide on a gardener’s skin to be carried accidentally
into his or her bloodstream. Another complication is that
DMSO is reduced in the body to dimethyl sulﬁde, a
compound with a strong garlic-like odor that soon appears
on the breath.

114
The FDA has approved DMSO for use in certain
bladder conditions and as a veterinary drug for
topical use in nonbreeding dogs and horses. For
example, DMSO is used as an anti-inﬂammatory
rub for race horses.

End of Chapter 5
Aldehydes and Ketones
General, Organic, and Biological Chemistry,Fifth Edition
H. Stephen Stoker
Brroks/Cole Cengage Learning. Permission required for reproduction or display.

Chapter 5 Aldehydes and Ketones

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