Transcript 23.3 Carbonyl Compounds

23.3 Carbonyl Compounds >
Chapter 23
Functional Groups
23.1 Introduction to Functional
Groups
23.2 Alcohols, Ethers, and Amines
23.3 Carbonyl Compounds
23.4 Polymers
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23.3 Carbonyl Compounds >
CHEMISTRY
& YOU
What gives a banana its characteristic
smell?
Many organic
molecules
have pleasant
aromas.
2
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23.3 Carbonyl Compounds > Aldehydes and Ketones
Aldehydes and Ketones
What structural characteristic do an
aldehyde and a ketone share?
3
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23.3 Carbonyl Compounds > Aldehydes and Ketones
An oxygen atom can also be bonded to
a single carbon atom by a double
covalent bond.
• A carbonyl group is a functional group
with the general structure C O.
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23.3 Carbonyl Compounds > Aldehydes and Ketones
The C O functional group is present
in aldehydes and ketones.
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23.3 Carbonyl Compounds > Aldehydes and Ketones
An aldehyde is an organic compound in
which the carbon of the carbonyl group is
joined to at least one hydrogen.
• The general formula of
an aldehyde is RCHO.
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23.3 Carbonyl Compounds > Aldehydes and Ketones
A ketone is an organic compound in which
the carbon of the carbonyl group is joined
to two other carbons.
• The general formula
of a ketone is
RCOR.
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23.3 Carbonyl Compounds > Aldehydes and Ketones
The IUPAC system may be used for
naming aldehydes and ketones.
• First identify the longest carbon chain that
contains the carbonyl group.
• Replace the -e ending of the parent
structure with -al to designate an aldehyde.
– In the IUPAC system, the continuous chain
aldehydes are named methanal, ethanal,
propanal, butanal, and so forth.
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23.3 Carbonyl Compounds > Aldehydes and Ketones
The IUPAC system may be used for naming
aldehydes and ketones.
• Ketones are named by changing the ending of
the longest continuous carbon that contains
the carbonyl group from -e to -one.
– If the carbonyl group of a ketone could occur at
more than one place on the chain, then its position
is designated by the lowest possible number.
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23.3 Carbonyl Compounds >
Interpret Data
Some Common Aldehydes
IUPAC name
(common name)
Structural formula
Ball-and-stick
model
Methanal
(formaldehyde)
Ethanal
(acetaldehyde)
Benzaldehyde
(benzaldehyde)
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23.3 Carbonyl Compounds >
Interpret Data
Some Common Ketones
IUPAC name
(common name)
Structural formula
Ball-and-stick model
Propanone
(acetone)
Diphenylmethanone
(benzophenone)
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23.3 Carbonyl Compounds > Aldehydes and Ketones
Uses of Aldehydes and Ketones
The simplest aldehyde is methanal
(HCHO), also called formaldehyde.
• Its greatest use is in the manufacture of
synthetic resins.
• A 40% aqueous solution of methanal,
known as formalin, can be used to
preserve biological specimens.
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23.3 Carbonyl Compounds > Aldehydes and Ketones
Uses of Aldehydes and Ketones
The most common industrial ketone is
propanone, also called acetone.
• Propanone is used in industry as a solvent
for resins, plastics, and varnishes.
• Many nail-polish removers contain
propanone as well.
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23.3 Carbonyl Compounds > Aldehydes and Ketones
Uses of Aldehydes and Ketones
A wide variety of aldehydes and ketones
have been isolated from plants and
animals. Many have fragrant odors.
• Benzaldehyde is also known as oil of
bitter almond because it is largely
responsible for the taste and aroma of
almonds.
• Many flavoring agents, including
vanilla bean extract and cinnamon
sticks, contain aromatic aldehydes.
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23.3 Carbonyl Compounds > Aldehydes and Ketones
Properties of Aldehydes and Ketones
• Aldehydes and ketones cannot form
intermolecular hydrogen bonds because
they lack —OH and —NH groups.
– They have boiling points that are lower than
those of corresponding alcohols.
• Aldehydes and ketones can attract each
other, however, through polar-polar
interactions of their carbonyl groups.
– Their boiling points are higher than those of the
corresponding alkanes.
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23.3 Carbonyl Compounds >
Interpret Data
Some Organic Compounds with Three Carbons
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Boiling Point
(°C)
Primary
intermolecular
interactions
Compound
Formula
Propane
CH3CH2CH3
–42
Dispersion
forces
Propanal
CH3CH2CHO
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Polar-polar
interactions
Propanone
CH3COCH3
56
Polar-polar
interactions
1-Propanol
CH3CH2CH2OH
97
Hydrogen
bonding
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23.3 Carbonyl Compounds > Aldehydes and Ketones
Properties of Aldehydes and Ketones
• Aldehydes and ketones can form weak
hydrogen bonds between the carbonyl oxygen
and the hydrogen atoms of water.
– The lower members of the series—up to three
carbons—are soluble in water in all proportions.
– As the length of the hydrocarbon chain increases
above four, however, water solubility decreases.
• As might be expected, all aldehydes and
ketones are soluble in nonpolar solvents.
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23.3 Carbonyl Compounds >
Why do aldehydes and ketones have similar
properties?
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23.3 Carbonyl Compounds >
Why do aldehydes and ketones have similar
properties?
Aldehydes and ketones have similar properties
because each contains a C O functional
group.
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23.3 Carbonyl Compounds > Carboxylic Acids
Carboxylic Acids
What is the general formula of a
carboxylic acid?
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23.3 Carbonyl Compounds > Carboxylic Acids
• A carboxyl group is a functional group that
consists of a carbonyl group attached to a
hydroxy group.
– It can be written as —COOH or —CO2H.
• A carboxylic acid is an organic compound
with a carboxyl group.
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23.3 Carbonyl Compounds > Carboxylic Acids
The general formula of a carboxylic
acid is RCOOH.
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23.3 Carbonyl Compounds > Carboxylic Acids
Carboxylic acids are considered weak
acids because they ionize weakly in
solution.
• In water, they can lose a hydrogen ion and
form a carboxylate ion, as shown in the
following reaction.
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23.3 Carbonyl Compounds > Carboxylic Acids
In the IUPAC system, carboxylic acids are
named by replacing the -e ending of the
parent structure with the ending -oic acid.
• Remember, the parent hydrocarbon of a
carboxylic acid is the longest continuous
carbon chain containing the carboxyl group.
• The carboxylic acid CH3COOH
is named ethanoic acid.
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23.3 Carbonyl Compounds >
Interpret Data
Some Saturated Aliphatic Carboxylic Acids
Molecular
formula
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Carbon
IUPAC name
atoms
Common
name
Melting
point (°C)
HCOOH
1
Methanoic acid
Formic acid
8
CH3COOH
2
Ethanoic acid
Acetic acid
17
CH3CH2COOH
3
Propanoic acid
Propionic acid
CH3(CH2)2COOH
4
Butanoic acid
Butyric acid
–6
CH3(CH2)4COOH
6
Hexanoic acid
Caproic acid
–3
CH3(CH2)6COOH
8
Octanoic acid
Caprylic acid
16
CH3(CH2)8COOH
10
Decanoic acid
Capric acid
31
CH3(CH2)10COOH
12
Dodecanoic acid
Lauric acid
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CH3(CH2)12COOH
14
Tetradecanoic acid
Myristic acid
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CH3(CH2)14COOH
16
Hexadecanoic acid Palmitic acid
63
CH3(CH2)16COOH
18
Octadecanoic acid
70
Stearic acid
–22
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23.3 Carbonyl Compounds > Carboxylic Acids
Lemons and limes contain citric acid, a
carboxylic acid that gives citrus fruits their
sour flavor.
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23.3 Carbonyl Compounds > Carboxylic Acids
Many carboxylic acids were first isolated
from fats and are called fatty acids.
• Propionic acid, the three-carbon acid, literally
means first fatty acid.
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23.3 Carbonyl Compounds > Carboxylic Acids
Like alcohols, carboxylic acids form intermolecular
hydrogen bonds.
• Thus, carboxylic acids have higher boiling and melting
points than other compounds of similar molar mass.
• The low-molar-mass members of the aliphatic
carboxylic acid series are colorless, volatile liquids.
• The higher members of the series are nonvolatile,
waxy solids with low melting points.
• All aromatic carboxylic acids are solids at room
temperature.
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23.3 Carbonyl Compounds > Carboxylic Acids
The carboxyl group in carboxylic acids is
polar and readily forms hydrogen bonds
with water molecules.
• Methanoic, ethanoic, propanoic, and butanoic
acids are completely soluble in water.
• After four carbons, however, the solubility
drops sharply.
• Most carboxylic acids are also soluble in
organic solvents such as ethanol or
propanone.
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23.3 Carbonyl Compounds >
What is a fatty acid?
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23.3 Carbonyl Compounds >
What is a fatty acid?
A fatty acid is a carboxylic acid that was
first isolated from fats.
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Oxidation-Reduction
23.3 Carbonyl Compounds >
Reactions
Oxidation-Reduction Reactions
Why is dehydrogenation classified as
an oxidation reaction?
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Oxidation-Reduction
23.3 Carbonyl Compounds >
Reactions
The classes of organic compounds you
have just studied—aldehydes, ketones,
and carboxylic acids—are related by
oxidation and reduction reactions.
• Oxidation is the gain of oxygen, loss of
hydrogen, or loss of electrons.
• Reduction is the loss of oxygen, gain of
hydrogen, or gain of electrons.
• One does not occur without the other.
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Oxidation-Reduction
23.3 Carbonyl Compounds >
Reactions
In organic chemistry, the number of
oxygen atoms and hydrogen atoms
attached to carbon indicates the degree of
oxidation of a compound.
• The fewer hydrogens on a carbon-carbon
bond, the more oxidized the bond.
• Thus, a triple bond is more oxidized than a
double bond, which is more oxidized than a
single bond.
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Oxidation-Reduction
23.3 Carbonyl Compounds >
Reactions
The loss of a molecule of hydrogen from
an organic molecule is called a
dehydrogenation reaction.
• It is the opposite of a hydrogenation reaction.
• Strong heating and a catalyst are usually
needed to make dehydrogenation reactions
occur.
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Oxidation-Reduction
23.3 Carbonyl Compounds >
Reactions
Dehydrogenation is an oxidation reaction
because the loss of each molecule of
hydrogen involves the loss of two
electrons from the organic molecule.
• The remaining carbon electrons pair to
make a second or third bond.
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Oxidation-Reduction
23.3 Carbonyl Compounds >
Reactions
Oxidation in organic chemistry also involves the
number and degree of oxidation of oxygen
atoms attached to the carbon atom.
• Methane, a saturated hydrocarbon, can be oxidized in
steps to carbon dioxide.
• Methane is oxidized to methanol, then to methanal,
then to methanoic acid, and finally to carbon dioxide.
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Oxidation-Reduction
23.3 Carbonyl Compounds >
Reactions
The more reduced a carbon compound is,
the more energy it can release upon its
complete oxidation to carbon dioxide.
• The oxidation of organic compounds is
exothermic.
• The energy-releasing properties of oxidation
reactions are extremely important for the
production of energy in living systems.
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Oxidation-Reduction
23.3 Carbonyl Compounds >
Reactions
Primary alcohols can be oxidized to
aldehydes.
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Oxidation-Reduction
23.3 Carbonyl Compounds >
Reactions
Secondary alcohols can be oxidized to
ketones by warming them with acidified
potassium dichromate (K2Cr2O7).
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Oxidation-Reduction
23.3 Carbonyl Compounds >
Reactions
Tertiary alcohols, however, cannot be
oxidized because there is no hydrogen
atom present on the carbon atom attached
to the hydroxy group.
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Oxidation-Reduction
23.3 Carbonyl Compounds >
Reactions
Aldehydes are so easily oxidized that it is
difficult to prevent further oxidation to
carboxylic acids.
• Further oxidation is avoided by removing
aldehydes from the reaction mixture as they
are formed.
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Oxidation-Reduction
23.3 Carbonyl Compounds >
Reactions
Tests for aldehydes make use of the ease with
which these compounds are oxidized.
• Benedict’s and Fehling’s reagents are
deep-blue alkaline solutions of
copper(II) sulfate.
• When an aldehyde is oxidized with
Benedict’s or Fehling’s reagent, a red
precipitate of copper(I) oxide is
formed.
• The aldehyde is oxidized to its acid,
and copper (II) ions are reduced to
copper(I) ions.
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23.3 Carbonyl Compounds >
What hydrocarbon can be oxidized to
form aldehydes? What hydrocarbon
can be oxidized to ketones?
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23.3 Carbonyl Compounds >
What hydrocarbon can be oxidized to
form aldehydes? What hydrocarbon
can be oxidized to ketones?
A primary alcohol can be oxidized to an
aldehyde. A secondary alcohol can be
oxidized to a ketone.
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23.3 Carbonyl Compounds > Esters
Esters
What is the general formula of an
ester?
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23.3 Carbonyl Compounds > Esters
Esters are probably the most pleasant
and delicious organic compounds one can
study.
• Many esters have pleasant, fruity odors.
• Esters give blueberries, pineapples, apples,
pears, bananas, and many other
fruits their characteristic aromas.
• They also give many perfumes
their fragrances.
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23.3 Carbonyl Compounds > Esters
An ester is an organic compound in which
the —OH of the carboxyl group has been
replaced by an —OR from an alcohol.
• Esters contain a carbonyl group and an ether
link to the carbonyl carbon.
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23.3 Carbonyl Compounds > Esters
The general formula of an ester is
RCOOR.
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23.3 Carbonyl Compounds >
CHEMISTRY
& YOU
The smell of strawberries is largely due to benzyl
acetate. The smell of almonds is largely due to
benzaldehyde. How are the general formulas of
these compounds similar? How are they
different?
50
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23.3 Carbonyl Compounds >
CHEMISTRY
& YOU
The smell of strawberries is largely due to benzyl
acetate. The smell of almonds is largely due to
benzaldehyde. How are the general formulas of
these compounds similar? How are they
different?
Benzyl acetate and
benzaldehyde each contain
a benzene ring. Benzyl
acetate contains an ester
group, while benzaldehyde
contains an aldehyde
group.
51
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23.3 Carbonyl Compounds > Esters
Although ester molecules are polar, they
cannot form hydrogen bonds with one
another.
• They do not contain hydrogen attached to
oxygen or another electronegative atom.
• As a result, only weak attractions hold ester
molecules to one another.
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23.3 Carbonyl Compounds > Esters
Although ester molecules are polar, they
cannot form hydrogen bonds with one
another.
• They do not contain hydrogen attached to
oxygen or another electronegative atom.
• As a result, only weak attractions hold ester
molecules to one another.
– Esters have much lower boiling points than
carboxylic acids.
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23.3 Carbonyl Compounds > Esters
Although ester molecules are polar, they
cannot form hydrogen bonds with one
another.
• The low-molar-mass esters are somewhat
soluble in water, but esters containing more
than four or five carbons have very limited
solubility.
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23.3 Carbonyl Compounds > Esters
Esters may be prepared from a carboxylic
acid and an alcohol.
• The process is called esterification.
• The reactants, usually a carboxylic acid and
a primary or secondary alcohol, are heated
with an acid as a catalyst.
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23.3 Carbonyl Compounds > Esters
If an ester is heated with water for several
hours, usually very little happens.
• In strong acid or base solutions, however, the
ester breaks down.
• An ester is hydrolyzed by the addition of
water to produce a carboxylic acid and an
alcohol.
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23.3 Carbonyl Compounds > Esters
Hydroxide ions also promote this reaction.
• Because many esters do not dissolve in
water, a solvent such as ethanol is added to
make the solution homogeneous.
• The reaction mixture is usually heated.
• All of the ester is converted to products.
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23.3 Carbonyl Compounds > Esters
If the reaction mixture is acidified, the
carboxylic acid forms.
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23.3 Carbonyl Compounds >
What are reactants in an esterification
reaction? What are the products?
59
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23.3 Carbonyl Compounds >
What are reactants in an esterification
reaction? What are the products?
The reactants in an esterification reaction are a
carboxylic acid and an alcohol. The products
are an ester and water.
60
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23.3 Carbonyl Compounds > Key Concepts
The C O functional group is present in
aldehydes and ketones.
The general formula of a carboxylic acid is
RCOOH.
Dehydrogenation is an oxidation reaction
because the loss of each molecule of
hydrogen involves the loss of two
electrons from the organic molecule.
The general formula of an ester is RCOOR.
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23.3 Carbonyl Compounds > Glossary Terms
• carbonyl group: a functional group having a
carbon atom and an oxygen atom joined by a
double bond; it is found in aldehydes,
ketones, esters, and amides
• aldehyde: an organic compound in which the
carbon of the carbonyl group is joined to at
least one hydrogen; the general formula is
RCHO
• ketone: an organic compound in which the
carbon of the carbonyl group is joined to two
other carbons; the general formula is RCOR
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23.3 Carbonyl Compounds > Glossary Terms
• carboxyl group: a functional group
consisting of a carbonyl group attached to a
hydroxyl group; it is found in carboxylic acids
• carboxylic acid: an organic acid containing
a carboxyl group; the general formula is
RCOOH
• fatty acid: the name given to continuouschain carboxylic acids that were first isolated
from fats
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23.3 Carbonyl Compounds > Glossary Terms
• dehydrogenation reaction: a reaction in
which hydrogen is lost
• ester: a derivative of a carboxylic acid in
which the —OH of the carboxyl group has
been replaced by the —OR from an alcohol;
the general formula is RCOOR
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23.3 Carbonyl Compounds >
BIG IDEA
Carbon Chemistry and Reactions
• Chemical reactions can be used to
change the structure of organic
molecules, often by introducing a new
functional group.
• Oxidation-reduction reactions are
commonly used in organic chemistry.
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23.3 Carbonyl Compounds >
END OF 23.3
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