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Organic Chemistry
32
The Aldehydes & Ketones
Leaving Certificate Chemistry
The First 4 Aldehydes
Structural Formulae
Methanal: HCHO
O
―
―
1 CarbonLong
group present
―C ―H
O
H
C
H
The First 4 Aldehydes
Structural Formulae
Ethanal: CH3CHO
O
H
―
―
2 Carbons
Long
―C ―H
group present
H
O
C
C
H
H
The First 4 Aldehydes
Structural Formulae
Propanal: C2H5CHO
O
H
―
―
3 Carbons
Long
―C ―H
group present
H
H
O
C
C
C
H
H
H
The First 4 Aldehydes
Structural Formulae
Butanal: C3H7CHO
O
H
―
―
4 Carbons
Long
―C ―H
group present
H
H
H
O
C
C
C
C
H
H
H
H
O
H
C
Benzaldehyde
At room temperature
it is a colourless liquid
with a characteristic
and pleasant almondlike odour
Physical Properties of the aldehydes
1. Use electronegativity differences to predict what kinds of
bonds are present in an aldehyde such as ethanal. HINT USE THE RULES
2. Can you predict whether an aldehyde or its corresponding
alkane would have a higher boiling point? HINT - Think
about the intermolecular forces present
3. Can you explain why the boiling points of the aldehydes
increase with the length of the chain? HINT - Think about
the intermolecular forces present
4. Would the lower or higher members of the aldehydes be
more soluble in water? HINT – water is polar. LIKE
DISSOLVES LIKE
The First 2 Ketones
Structural Formulae
Propanone: CH3COCH3
O
H
H
C
H
―
―
3 Carbons
Long
C―C ―C
group present
O
C
H
C
H
H
Nail Varnish
Remover
An isomer of propanal
The First 2 Ketones
Structural Formulae
Butanone: CH3COC2H5
O
H
―
―
4 Carbons
Long
An isomer of butanal
C―C ―C
group present
H
O
H
H
C
C
C
C
H
H
H
H
Physical Properties of the ketones
1. Use electronegativity differences to predict what kinds of
bonds are present in an ketones such as propanone. HINT
- USE THE RULES
2. Can you predict whether an ketone or its corresponding
alkane would have a higher boiling point? HINT - Think
about the intermolecular forces present
3. Can you explain why the boiling points of the ketones
increase with the length of the chain? HINT - Think about
the intermolecular forces present
4. Would the lower or higher members of the ketones be more
soluble in water? HINT – water is polar. LIKE DISSOLVES
LIKE
Formation of
an aldehyde
or ketone
Oxidation of a primary
or secondary alcohol
Oxidation of a primary alcohol
Methanol CH3OH
H
H
C
O
Acidified Sodium
Dichromate
OH
H
C
C
Methanal
HCHO
O
H
H
OH
Methanoic Acid
HCOOH
Excess
H
Oxidation of a primary alcohol
Ethanol C2H5OH
H
H
H
C
C
H
H
O
H
H
C
H
C
Acidified Sodium
Dichromate
OH
OH
Excess
Ethanoic Acid
CH3COOH
H
H
O
C
C
H
Ethanal
CH3CHO
H
Oxidation of a primary alcohol
H
H
H
OH
H
C
C
C
H
H
H
Propanoic
Propanol
Propanal
Acid
C2CH23H
OH
5COOH
57CHO
O
OH
Acidified Sodium
Dichromate
Excess
Oxidation of a primary alcohol
H
H
H
H
H
OH
C
C
C
C
H
H
H
H
O
OH
Butanoic
Butanol
Butanal Acid
On reaction with acidified
sodium dichromate
In Excess
Substitution
using UV Light
The Alkanes
Ethane C2H6
+ H2
- H2
The Chloroalkanes
Chloroethane C2H5Cl
The Alkenes
+ HCl , + Cl2
Ethene C2H4
+ H2O
- H2O Aluminium Oxide
Catalyst
The Polymers
Polythene & Polypropene
The Alcohols
Ethanol C2H5OH
The Alcohols
Ethanol C2H5OH
Acidified sodium
dichromate
Hydrogen,
Nickel catalyst
Oxidation
Reduction
The Aldehydes
Ethanal CH3CHO
Acidified sodium
Reduction
dichromate
Hydrogen,
Oxidation
Nickel catalyst
The Carboxylic
Acids
Ethanoic Acid
CH3COOH
Oxidation of a secondary alcohol
H
H
O
OH
H
C
C
C
H
H
H
H
Acidified Sodium
Dichromate
Propanone
Propan-2-ol
Oxidation of a secondary
alcohol produces a ketone
Nail Varnish
Remover
Oxidation of a secondary alcohol
H
H
O
OH
H
H
C
C
C
C
H
H
H
H
Butanone
Butan-2-ol
Oxidation of a secondary
alcohol produces a ketone
H
Acidified
Sodium
Dichromate
Oxidation of a secondary alcohol
Acidified sodium dichromate The
The Alcohols
Ethanol C2H5OH
Hydrogen,
Nickel catalyst
Ketones
Propanone from
propan-2-ol
Acidified sodium
dichromate
Oxidation
H2, Ni Reduction
Reduction
The Aldehydes
Ethanal CH3CHO
Acidified sodium
Reduction
dichromate
Hydrogen,
Oxidation
Nickel catalyst
The Carboxylic
Acids
Ethanoic Acid
CH3COOH
No reaction occurs
with a ketone
Tests to distinguish between an aldehyde
and a ketone
Acidified Potassium Permanganate
Add 5 cm3 of Acidified
potassium
H permanganate
O
HAdd 2C cm3 C
OH
of ethanal
(aldehyde), heat and shake
Test
tube
Heat
H
The pink colour turns
colurless
Ethanoico
acid formed
CH3COOH
No reaction occurs
with a ketone
Tests to distinguish between an aldehyde
and a ketone
Fehling’s Test
Add 1 cm3 of Fehling’s No. 1
3 of Fehling’s No. 2
& 1 cmH
O
solutions
Test
tube
Heat
HAdd 1Ccm3 C
OH
of ethanal
(aldehyde), heat and shake
H
A brick red precipitate is
observed
Ethanoic
acid formed
CH3COOH
No reaction occurs
with a ketone
Tests to distinguish between an aldehyde
and a ketone
Tollen’s Reagent
Add 3 cm3 of Silver Nitrate
3 of
solution
and
1
cm
H
O
Sodium Hydroxide solution
H
C
C
OH
Add a few drops of ammonia
solution and shake. Then
add 4-5 drops
H
of ethanal and
heat water bath
Test
tube
Heat
Ethanoic
acidisformed
A “silver
mirror”
observed
CH3COOH
• Watch video on you tube http://www.youtube.com/watch?v=TRFkU
6442oo
• See animations videos
• http://youtu.be/qDGCE-KXPhw fehlings
test
• http://youtu.be/zFMsqcGdZCc silver
mirror test
• And http://youtu.be/CMCVpE8p8yo