Aldehydes and Ketones

1
Aldehydes and Ketones
Structure and Bonding Nomenclature Order of
Precedence Physical Properties Addition of
Alcohols
2
Aldehydes and Ketones

• In an aldehyde, an H atom is attached to a
  carbonyl group (written linearly it is RCHO)
• O carbonyl group
• ?
• CH3-C-H
• In a ketone, two carbon groups are attached to a
  carbonyl group (written linearly it is RCOR)
• O carbonyl group
• ?
• CH3-C-CH3

3
Naming Aldehydes

• IUPAC Replace the -e in the alkane name with al
• O O O
• ? ? ?
• H-C-H CH3-C-H CH3CH2C-H
• methanal ethanal propanal

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Naming Aldehydes

• Name the longest carbon chain containing the
  carbonyl as the parent by replacing the -e of the
  alkane name with -al
• Number the chain to give the carbon atom of the
  carbonyl group 1
• Assemble the rest of the name the same way used
  in naming alcohols except do not include 1 to
  specify the location
• 
  2- ethylpentanal

• O
• ?
  CH3CH2CHCH
• CH3CH2CH2

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Aldehydes as Flavorings
O
O
C
H
C
H

C
H
C
H
H
O
O
C
H
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6
Glucose is an aldehyde
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Naming Ketones

• The parent is the longest carbon chain that
  includes the carbonyl
• Name the parent by replacing the -e of the alkane
  name with -one
• Number the parent such the the carbonyl gets the
  lowest location number possible
• Assemble the remainder of the same as before
• O O
• ? ?
• CH3 -C-CH3 CH3-C-CH2-CH3
• Propanone 2-Butanone

8
Ketones

• O O
• ? ?
• Butter flavor CH3-C-C-CH3 butanedione
• O
• ?
• Clove flavor CH3-C-CH2CH2CH2CH2CH3
• 2-heptanone

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Order of Precedence

• O O
• ? ?
  
• CH3CCH2CH 3-oxobutanal
• O
• ?
  
• CH3CHCH 2-hydroxypropanal
• OH

10
Fructose is a Ketone

11
Ketones as Hormones
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Learning Check AK 1

• Classify each as an aldehyde (1), ketone (2) or
  neither(3).
• O
• ?
• A. CH3CH2CCH3 B. CH3-O-CH3
• CH3 O
• ?
• C. CH3-C-CH2CH D.
• CH3

O
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Solution AK 1

• Classify each as an aldehyde (1), ketone (2) or
  neither(3).
• O
• ?
• A. CH3CH2CCH3 2 B. CH3-O-CH3 3
• CH3 O
• ?
• C. CH3-C-CH2CH 1 D. 2
• CH3

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Learning Check AK 2

• Name the following
• O
• ?
• A. CH3CH2CCH3 B.
• CH3 O
• ?
• C. CH3-C-CH2CH
• CH3

O
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Solution AK 2

• O
• ?
• A. CH3CH2CCH3 B.
• 2-butanone
• CH3 O
• ?
• C. CH3-C-CH2CH
• cyclohexanone
• CH3
• 3,3-dimethylbutanal

O
16
Learning Check AK 3

• Draw the structural formulas for each
• A. 3-Methylpentanal
• B. 2,3-Dibromopropanal
• C. 3-Methyl-2-butanone

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Solution AK 3

• Draw the structural formulas for each
• CH3 O
  ?
• A. 3-Methylpentanal CH3CH2CHCH2CH
• Br O
• ?
• B. 2,3-Dibromopropanal Br-CH2CHCH
• 
  O
• ?
• C. 3-Methyl-2-butanone CH3CHCCH3
• CH3

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Order of Precedence
Increasing Precedence
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Physical Properties

• The carbonyl group is planar, unsaturated, and
  moderately polar
• Due to the polarity of the CO group, aldehydes
  and ketones are moderately polar compounds

Oxygen is more electronegative than carbon
therefore it has a permanent d- charge
d-
d
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Physical Properties

• Molecules are attracted to each other
• Attraction not as strong as with OH
• Cannot donate hydrogen bonds, only accepts
• Boil higher than alkanes but lower than alcohols

21
Physical Properties- BP
22
Physical Properties- Solubility

• Soluble in water for lower weight compounds
• As carbon chain length increases, solubility
  decreases

d
R
d
CO
d-
R
23
Review - Oxidation

• Is a gain of oxygen (O)
• or
• A loss of hydrogen (H)

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Review - Oxidation

• 1alcohols are oxidized to aldehydes and 2
  alcohols are oxidized to ketones
• Alcohols
• 1 2
• aldehydes ketones

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Review - Oxidation

• Primary alcohol O aldehyde
• OH O
• CH3-C-H KMnO4 CH3-C-H
• H
• Ethanol Ethanal

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Review - Oxidation

• O
• Secondary alcohol ketone
• OH O
• KMnO4
• CH3-C-CH3 CH3-C-CH3
• 2-Propanol 2-propanone

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Review - Oxidation

• O
• Tertiary alcohols no reaction
• OH O
• CH3-C-CH3 no product
• CH3 no H on the C-OH to oxidize
• 2-Methyl-2-propanol

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Tollens Test

• Also called the Silver Mirror Test
• The aldehyde group is easily oxidized to the
  carboxylic acid group, but the ketone is
  difficult to oxidize
• Tollens Test simple test for the presence of
  aldehyde
• Uses mild oxidizing agent (Tollens Reagent)
  AgNO3 and NH3 in H2O

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Tollens Test

• Tollens Reagent oxidizes aldehydes
• When reaction occurs in a thoroughly clean test
  tube the silver plates to form beautiful mirror

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Reduction

• Is a loss of oxygen (O)
• or
• gain of hydrogen (H)

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Reduction

• Aldehydes are reduced to 1 alcohols and ketones
  are reduced to 2 alcohols
• Alcohols
• 1 2
• aldehydes ketones

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Reduction

• Aldehydes and Ketones are reduced to alcohols
  when hydrogens add to their carbonyl groups
• Aldehyde H2 1o alcohol

Metal Catalyst
Ketone H2 2o alcohol
Metal Catalyst
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Reduction

• Ni
• Aldehyde H2 Alcohol
• O OH
• ? Ni
• CH3-C-H H2 CH3-C-H
• 
  H
• Ethanal Ethanol

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Reduction

• Ni
• Ketone H2 Secondary alcohol
  O OH
• Ni
• CH3-C-CH3 CH3-CH-CH3
• 2-Propanone 2-propanol

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Oxidation and Reduction
REDUCTION OF ALDEHYDES AND KETONES
2H 2e-
C
O
C
O
H
H
OXIDATION OF ALCOHOLS
- 2H - 2e-
C
O
C
O
H
H
These two reactions are the inverse of each other!
36
Reactions

• Carbonyl groups have a double bond therefore
  they can undergo addition reactions
• Alcohols add to the carbonyl group of aldehydes
  and ketone

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Hemiacetals

• Hemiacetal molecule that has a carbon atom
  holding both an -OH (alcohol) and -OR (alkoxy)
  group
• Is formed when an alcohol adds to the carbonyl of
  an aldehyde or ketone
• Occurs when the -H goes to the carbonyl O and the
  OR goes to the carbonyl C

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Hemiacetal Formation
R
ROH
C
O
aldehyde
H
hemiacetal
R
R
O
H
ROH
C
C
O
O
R
ketone
R
R
39
Hemiacetal Formation
addition of one mole
O
O
H
H
hemiacetal
C

CH3OH
R
C
R
'
CH3
CH3
O
CH3
40
Acetals

• Acetal molecule that has a carbon atom holding
  2 -OR (alkoxy) groups
• Is formed when an alcohol adds to a hemiacetal in
  the presence of acid catalyst
• Is a substitution reaction since the OH of the
  is replaced with OR from the alcohol
• Is a condensation reaction since water is produced

41
Acetal Formation
Hemiacetals can react further w/ alcohols to form
acetals and water
O
H
O
R
H

O

R
C
R
'
R
O
H
R
C
R
'
H
H
O
R
O
R
an acetal
O
H
O
CH3
H
CH3

O

C
CH3
'
R
C
R
'
H
CH3 OH
O
CH3
O
CH3
H
an acetal
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Acetals and Hemiacetals
R
R
O
R
ROH
ROH
C
O
C
O
R
aldehyde
H
H
hemiacetal
acetal
R
R
R
O
H
O
R
ROH
ROH
C
C
O
C
O
R
O
R
ketone
R
R
R