Transcript Chapter_Sixteen_lecture

Chapter Sixteen
Aldehydes and Ketones
Goals
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Be able to recognize the carbonyl group and describe its
polarity and shape.
Be able to name the members of these families and write
their structures, given the names.
Be able to describe such properties as polarity, hydrogen
bonding, and water solubility.
Be able to specify where aldehydes and ketones are found &
list their major applications
Be able to describe and predict the products of the oxidation
and reduction of aldehydes and ketones.
Be able to recognize hemiacetals and acetals, describe the
conditions under which they are formed, and predict the
products of hemiacetal and acetal formation and acetal
hydrolysis
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The Carbonyl Group
• Any compound that contains a carbonyl
group, C=O.
– The bond angles between the three substituents
on the carbonyl carbon atom are 120°, or close to
it.
Carbonyl group: A
functional group that
has a C atom joined to
an O atom by a double
bond.
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Aldehydes and Ketones
Aldehyde: A compound that
has a carbonyl group bonded
to at least one hydrogen.
Ketone: A compound
that has a carbonyl
group bonded to two
carbons in organic
groups that can be the
same or different.
Naming Aldehydes and Ketones
Simple aldehydes are known by their common names, which
end in –aldehyde
The naming convention is to replace the alkane “ – e”
ending is replaced by –al
When substitute groups are
present, number the chain is
with 1 on the carbon
containing the for the
carbonyl group
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Naming
Ketones
1. Common names for ketones give
the names of the two alkyl groups
bonded to the carbonyl carbon
followed by the word ketone.
1. The location of the carbonyl group
is indicated by placing the number
of the carbonyl carbon in front of
the name.
2. Why is this a Ketone?
Properties of Aldehydes and Ketones
• Do not form hydrogen-bonds so they have lower
boiling than alcohols.
– higher boiling than alkanes because of the polarity of
the carbonyl group.
– Common aldehydes and ketones are liquids.
• Simple aldehydes and ketones are water-soluble due to
hydrogen bonding with water molecules, and ketones
are good solvents.
• Simple ketones are less toxic than simple aldehydes.
• Many aldehydes and ketones have distinctive odors.
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A perfumer sits at a
mixing table testing
new combinations of
fragrances, many of
which are aldehydes
and ketones.
Copyright © 2010 Pearson
Education, Inc.
Chapter Sixteen
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Some Common Aldehydes and Ketones
• Formaldehyde a colorless gas.
– causes eye, throat, and bronchial
irritation,
– In High concentration, can trigger
asthma attacks.
– dermatitis. CH2O is very toxic by
ingestion, causing serious kidney
damage, coma, and sometimes even
death.
• kills viruses, fungi, and bacteria by
reaction with the groups in proteins,
allowing for its use in disinfecting
and sterilizing equipment and as a
preservative for biological
specimens.
Plastics
1. The first successful synthetic plastic was a
polymer of phenol and formaldehyde known as
Bakelite
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Once widely used for such items as pot handles,
fountain pens, and cameras.
Urea–formaldehyde polymers are now more widely
used than Bakelite.
CH2O polymers release CH2O
into the air. Concerns over the
toxicity and possible
carcinogenicity of CH2O limits
most household applications.
Acetaldehyde
A is a sweet-smelling,
flammable liquid present in ripe
fruits, and produced in the
normal breakdown of
carbohydrates.
General narcotic, and large doses can cause
respiratory failure. Chronic exposure
produces symptoms like those of alcoholism
*product of alcohol metabolism, broken down
by acetaldehyde dehydrogenase.
1. one of the most widely used of all
organic solvents.
2. It dissolves most organic
compounds and is also miscible
with water.
3. Acetone is the solvent in many
varnishes, lacquers, and nail polish
removers.
Acetone
Acetone on a patient’s breath is indicative of a
metabolic imbalance of fats and carbohydrates:
starvation or diabetes mellitus
Acetone is produced in the liver, a condition known
as ketosis that in severe cases leaves the odor of
acetone on a patient’s breath.
Oxidation of Aldehydes Produces a
carboxylic acid
1. Aldehyde oxidation results in replacing the hydrogen
bonded to the carbonyl carbon with a –OH group.
2. Ketones, do not have this hydrogen and do not react
with mild oxidizing agents.
• (a) In the Tollens’ test, colorless silver ion is
reduced to metallic silver.
• (b) In the Benedict’s test, the blue copper(II)
ion is reduced to copper(I) in brick-red
copper(I) oxide
• In both tests, the aldehyde is oxidized to
the carboxylic acid.
Reduction of Aldehydes and Ketones
Produces an Alcohol
• The reduction of a carbonyl group occurs with the
addition of hydrogen across the double bond to
produce an –OH group, a reaction that is the
reverse of the oxidation of an alcohol.
• Aldehydes are reduced to primary alcohols, and
ketones are reduced to secondary alcohols.
Addition of Alcohols: Hemiacetals and
Acetals
The initial product of addition reactions of aldehydes
and ketones with alcohols are known as hemiacetals.
Compounds with both an -OH group and an -OR
group bonded to the same carbon atom.
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Ethanol forms hemiacetals with acetaldehyde
and acetone.
– Hemiacetals rapidly revert back to aldehydes or
ketones by loss of alcohol and establish an
equilibrium with the aldehyde or ketone.
– When equilibrium is reached, very little hemiacetal
is present.
A major exception
• when the alcohol and carbonyl functional groups
that react are part of the same molecule.
• The resulting cyclic hemiacetal is more
• Most simple sugars exist mainly in the cyclic
hemiacetal form,
Acetal formation
• Addition of a acid catalyst is added to the
reaction of an alcohol with an aldehyde or
ketone, the hemiacetal initially formed is
converted into an acetal in a substitution
reaction.
An acetal is a compound that has two -OR groups bonded to what was
once the carbonyl carbon atom
The aldehyde or ketone from which an acetyl is
formed can be regenerated by reversing the
reaction. Reversal requires an acid catalyst and a
large quantity of water.
Hydrolysis: A reaction in which a bond or bonds are broken
and the -H and -OH of water add to the atoms of the broken
bond or bonds.