Download Chapter 14_CHEM131

Spencer L. Seager
Michael R. Slabaugh
www.cengage.com/chemistry/seager
Chapter 14
Aldehydes and Ketones
Jennifer P. Harris
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.
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:
3-bromobutanal
2-ethylbutanal
COMMON ALDEHYDES
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:
3-methyl-2-pentanone
2-methylcyclohexanone
COMMON KETONES
PHYSICAL PROPERTIES
• The carbonyl group is moderately polar, but it doesn’t have
any hydrogen atoms bonded to the oxygen atom, so it cannot
hydrogen bond between molecules.
PHYSICAL PROPERTIES (continued)
• 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.
PHYSICAL PROPERTIES (continued)
PHYSICAL PROPERTIES (continued)
• The C=O group can hydrogen bond with water molecules
because the oxygen atom in the carbonyl group has a partial
negative charge that attracts the partial positive charge of a
hydrogen atom in the water molecule.
• This makes low molecular weight aldehydes and ketones
water soluble (they have small hydrophobic sections).
PHYSICAL PROPERTIES (continued)
ALDEHYDE AND KETONE REACTIONS
• Recall the oxidation of alcohols to produce aldehydes and
ketones:
ALDEHYDE AND KETONE REACTIONS
(continued)
• The difference in reactivity toward oxidation is the chief
reason why aldehydes and ketones are classified in
separated families.
ALDEHYDE AND KETONE REACTIONS
(continued)
• The ease with which aldehydes are oxidized allows us to
test for the presence of aldehydes with Tollens’ reagent or
Benedict’s reagent.
• In general, ketones fail to react with these reagents.
From left to right, three test tubes
containing potassium dichromate
(K2Cr2O7), acetone, and benzaldehyde.
After the addition of equal amounts
of K2Cr2O7, the acetone remains
unreacted, whereas the
benzaldehyde is oxidized.
ALDEHYDE AND KETONE REACTIONS
(continued)
• In the presence of aldehydes, Tollens’ reagent produces a
silver coating on glass.
• This method is used to produce mirrors and silver ornaments.
ALDEHYDE AND KETONE REACTIONS
(continued)
• In the presence of aldehydes, Benedict’s reagent produces
a red precipitate.
From left to right, three test
tubes containing Benedict’s
reagent, 0.5% glucose solution,
and 2.0% glucose solution.
The addition of Benedict’s
reagent from the first tube
produces colors (due to the
red Cu2O) that indicate the
amount of glucose present.
ALDEHYDE AND KETONE REACTIONS
(continued)
• The addition of H2 in the presence of catalysts.
ALDEHYDE AND KETONE REACTIONS
(continued)
• Examples:
ALDEHYDE AND KETONE REACTION MAP
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
IMPORTANT ALDEHYDES AND KETONES
(continued)
• Acetone
• Important organic solvent
• Used in such things as nail polish remover
• Miscible with water
IMPORTANT ALDEHYDES AND KETONES
(continued)
• Progesterone and testosterone (female and male sex
hormones) are ketones.
IMPORTANT ALDEHYDES AND KETONES
(continued)
• Some aldehydes and ketones are very fragrant and are
used in flavorings.
• Vanillin (vanilla)
• Cinnamaldehyde (cinnamon)
• Citral (citrus flavoring)
• Camphor (medicinal odor)
IMPORTANT ALDEHYDES AND KETONES
(continued)
IMPORTANT ALDEHYDES AND KETONES
(continued)