Chap 14: ALDEHYDES AND KETONES
• The carbonyl group:
• Aldehydes have at least one hydrogen attached to the
carbonyl group.
• Ketones have two carbons attached to the carbonyl group.
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NAMING ALDEHYDES
• Find the longest carbon chain that contains the aldehyde
group.
• Change ending of the root hydrocarbon name by dropping
–e and adding –al.
• All other branches and groups are named and located
using standard IUPAC system.
Examples:
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NAMING KETONES
• Find the longest chain that contains C=O.
• Using the root alkane name, drop the –e ending and
change to –one.
• Number the longest carbon chain so the C=O group has
the lowest number.
• Name and number other substituents as before.
Examples:
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PHYSICAL PROPERTIES
• The carbonyl group is moderately polar, but it doesn’t have
any hydrogen atoms attached, so it cannot hydrogen bond
between molecules.
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PHYSICAL PROPERTIES, cont.
• Because of the polarity of the C=O group, these groups
can interact, but the attraction is not as strong as hydrogen
bonding.
• This makes the boiling point of aldehydes and ketones
higher than alkanes, but lower than alcohols.
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PHYSICAL PROPERTIES, cont.
• The C=O group can hydrogen bond with water molecules.
H
O
||
R-C-R
O
H
• This makes low molecular weight aldehydes and ketones
water soluble (they have small hydrophobic sections).
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ALDEHYDE AND KETONE REACTIONS
• Recall the oxidation of alcohols to produce aldehydes and
ketones:
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REACTIONS, cont.
• The addition of H2 in the presence of catalysts.
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Examples:
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REACTIONS, cont.
• The addition of alcohols to aldehydes produces an
unstable hemiacetal intermediate.
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REACTIONS, cont.
• General formulas for:
Hemiacetals
Acetals
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REACTIONS, cont.
• The addition of alcohol to ketones produces an unstable
hemiketal intermediate.
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REACTIONS, cont.
• General formula for:
Hemiketal
Ketal
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REACTIONS, cont.
• Cyclical hemiacetals and hemiketals are more stable than
open chains and are important in carbohydrate chemistry.
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REACTIONS, cont.
• Acetals and ketals are stable, but may be converted back
to aldehydes and ketones through acid catalyzed
hydrolysis. Hydrolysis is the breakage of a bond by
reaction with water.
• Acetal hydrolysis:
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REACTIONS, cont.
• Ketal hydrolysis:
Specific Example:
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IMPORTANT ALDEHYDES AND KETONES
• Formaldehyde
Gas at room temperature
Formalin – 37% aqueous solution
Sterilizer
Embalming fluid
Starting material for plastics such as Formica and
Bakelite
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IMPORTANT ALDEHYDES AND KETONES, cont.
• Acetone
(propanone)
Important organic solvent
Used in such things as nail polish remover
Miscible with water
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IMPORTANT ALDEHYDES AND KETONES, cont.
• Progesterone and testosterone (female and male sex
hormones) are ketones.
• Some aldehydes and ketones are very fragrant and are
used in flavorings.
Vanillin (vanilla)
Cinnamaldehyde (cinnamon)
Citral (citrus flavoring)
Camphor (medicinal odor)
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