Download Aldehydes and Ketones

Chapter Fifteen
Aldehydes
And Ketones
Aldehydes and Ketones
In an aldehyde, an H atom is attached to a carbonyl group
O
carbonyl group

CH3-C-H
In a ketone, two carbon groups are attached to a carbonyl
group
O
carbonyl group

CH3-C-CH3
Chapter 15 | Slide 2 of 36
Chapter 15 | Slide 3 of 36
Ketones as Hormones
Chapter 15 | Slide 4 of 36
Aldehydes and Ketones cont’d
← Fig. 15.1
Aldehydes and ketones
are related to alcohols
in the same manner
that alkenes are related
to alkanes.
Chapter 15 | Slide 5 of 36
Aldehydes and Ketones
→ Fig. 15.3
Aldehydes and ketones
with the same number
of carbon atoms and
the same degree of
saturation are structural
isomers.
Chapter 15 | Slide 6 of 36
Naming Aldehydes
•
•
•
•
Aldehydes are named by replacing the “e” with “____.”
The parent chain must contain the –_______ group.
The –CHO carbon is always carbon ___.
When attached to a ring “carbaldehyde” is used.
O
O
3
5
O
propaneal
6
4
2
1
4-ethyl
2,5-dimethyl
2- hexen eal
cyclopentanecarbaldehyde
Chapter 15 | Slide 7 of 36
Aldehydes and Ketones cont’d
← Fig. 15.2
Benzaldehyde, the
simplest aromatic
aldehyde.
.
Chapter 15 | Slide 8 of 36
Naming Ketones
• Ketones are named by replacing the “e” with “_____.”
• The parent chain must contain the ______.
• Numbering begins nearer the ______.
O
7
O
6
5
4
3
2
1
5-ethyl
3,6-dimethyl
2- heptan eone
2- butan eone
Chapter 15 | Slide 9 of 36
Name these aldehydes/ketones.
O
O
3-penten-2-one
5-methyl-3-cyclohexenone
O
O
2-phenylpropanal
cyclohexanone
Chapter 15 | Slide 10 of 36
Aldehydes and Ketones cont’d
←C.C 15.1
←Wood Smoke contains
formaldehyde and causes
eyes to tear.
←Formaldehyde is a
lachrymator (eye irritant)
© Harvey Lloyd/Peter Arnold, Inc.
Chapter 15 | Slide 11 of 36
Aldehydes and Ketones cont’d
← Fig. 15.4
Formalin is used to
preserve biological
specimens.
© 2005 Norbert Wu / www.norbertwu.com
Chapter 15 | Slide 12 of 36
Aldehydes and Ketones
→ Fig. 15.5
The delightful odor of
melted butter is largely
due to butanedione.
© Steven Needham / Envision
Chapter 15 | Slide 13 of 36
Aldehydes and Ketones cont’d
Chapter 15 | Slide 14 of 36
Aldehydes and Ketones
Why are some aldehydes and ketones soluble in water?
Chapter 15 | Slide 15 of 36
Physical Properties
of Aldehydes and Ketones
• The polarity of the carbonyl group in aldehydes
and ketones, which is responsible for many of their
physical properties.
– They have boiling points _______ than alcohols but
_______ than alkanes.
• Why?
– Nonpolar < Polar (Dipole-dipole) <H-bonds
– _____ molecular weight aldehydes and ketones are
__________ in water
• Why not ________ molecular weight aldehydes and ketones?
– Most aldehydes and ketones have odors
Chapter 15 | Slide 16 of 36
Aldehydes and Ketones
Chapter 15 | Slide 17 of 36
Synthesis of Aldehydes and Ketones
O
• Oxidation of alcohols.
– Primary alcohols
yield aldehydes.
– Secondary alcohols
yield ketones.
From primary
alcohols
O
From secondary
alcohols
Chapter 15 | Slide 18 of 36
• Oxidation reactions:
OH
PCC
CH2Cl2
R
PCC = Pyridinium chlorochromate
OH
Na2Cr2O7, H2O, CH3CO2H
R
R
Chapter 15 | Slide 19 of 36
Oxidation of Aldehydes
• Ketones are unreactive to oxidation because
no hydrogens are on the carbon.
O
O
R
H
AgNO3
NH4OH
R
OH
O
AgNO3
NH4OH
R
No Reaction
R'
Chapter 15 | Slide 20 of 36
Reduction of Aldehydes and Ketones
• Reduction: Adding hydrogen across the carbonyl
– Aldehyde  primary alcohol
– Ketone  secondary alcohol
CH
CH2
O
+ H2 
H3C
H3C
O
OH
+ H2 
C
H3C
OH
CH3
CH
H3C
CH3
Chapter 15 | Slide 21 of 36
Addition Reactions
• Polar molecules can add to the carbonyl in
aldehydes and ketones
• The negative part of the added molecule adds to
the positive carbonyl carbon
• The positive part of the added molecule adds to
the negative carbonyl oxygen
• d+ d- d+ d• -C=O + X-Y  -C-O-X
Y
Chapter 15 | Slide 22 of 36
Acetal Formation
• Alcohols add to the carbonyl of aldehydes and
ketones
• The addition of two alcohols forms an acetal.
•
O
O-CH3
• CH3-C-H + 2 CH3-OH CH3-C-H + H2O
•
O-CH3
Hydrolysis of acetals yield the aldehyde or ketone and
the alcohols that originally formed the acetal
Chapter 15 | Slide 23 of 36
Hemiacetal Formation
• The addition of one alcohol to an aldehyde or
ketone forms an intermediate called a hemiacetal
• Usually, hemiacetals are unstable and hard to
isolate.
•
O
O-CH3
• CH3-C-H + 2 CH3-OH CH3-C-H + H2O
•
O-H
Chapter 15 | Slide 24 of 36
Aldehydes and Ketones
CC 15.3 Diabetes, aldehyde oxidation, and glucose testing
Chapter 15 | Slide 25 of 36
Tests for Distinguishing between
Aldehydes and Ketones
• Tollens’ test (AKA Silver Mirror test)
– Tollens’ reagent, which contains Ag+, reacts with
aldehydes, but not with ketones
– The aldehyde is oxidized and Ag+ is reduced to Ag,
which appears as a silver “mirror” in the test tube (or
reaction vessel)
Chapter 15 | Slide 26 of 36
Aldehydes and Ketones cont’d
Figs. 15.8 a-c
(a) An aqueous
solution of ethanal is
added to a solution of
silver nitrate.
(b) The solution
darkens as ethanal is
oxidized to ethanoic
acid.
(c) The inside of the
beaker becomes
coated with metallic
silver.
Chapter 15 | Slide 27 of 36
Tests for Distinguishing between
Aldehydes and Ketones
• Benedict’s Test
– Benedict’s reagent, which contains Cu+2, reacts with
aldehydes that have an adjacent OH group
– The aldehyde is oxidized and Cu+2 is reduced Cu2O,
which appears as a brick red solid in the test tube
– Ketones do not react.
Chapter 15 | Slide 28 of 36
Aldehydes and Ketones
→ Fig. 15.9
Benedict’s solution
turns brick red when an
aldehyde reacts with it.
Chapter 15 | Slide 29 of 36
Chapter 15 | Slide 30 of 36
Work on the following learning checks as homework.
Chapter 15 | Slide 31 of 36
Learning Check
Classify each as an aldehyde (1), ketone (2) or
neither(3).
O

A. CH3CH2CCH3
CH3
B. CH3-O-CH3
O

C. CH3-C-CH2CH
D.
CH3
Chapter 15 | Slide 32 of 36
Learning Check
Name the following
O

A. CH3CH2CCH3
B.
CH3 O

C. CH3-C-CH2CH
CH3
Chapter 15 | Slide 33 of 36
Learning Check
Draw the structural formulas for each:
A. 3-Methylpentanal
B. 2,3-Dichloropropanal
C. 3-Methyl-2-butanone
Chapter 15 | Slide 34 of 36
Learning Check
• Select the compound that would have the higher boiling
point
– A. CH3-CH2-CH3 or
CH3-CH2-OH
– B. CH3-CH2-OH or CH3-O-CH3
– C.
O
OR
Chapter 15 | Slide 35 of 36
Learning Check
• Are the following compounds soluble in water?
– A. CH3-CH2-CH3
– B. CH3-CH2-OH
– C.
O
– D.
O
Chapter 15 | Slide 36 of 36