1. ALDEHYDES & KETONES CONTENTS Prior knowledge
Bonding in carbonyl compounds
Structural differences
Nomenclature
Preparation
Identification
Oxidation
Nucleophilic addition
Reduction

2. Before you start it would be helpful to…
ALDEHYDES & KETONES
Before you start it would be helpful to…
know the functional groups found in organic chemistry
know the arrangement of bonds around carbon atoms
recall and explain the polarity of covalent bonds

3. CARBONYL COMPOUNDS - STRUCTURE
Structure carbonyl groups consists of
a carbon-oxygen double bond
the bond is polar due to the
difference in electronegativity
Difference ALDEHYDES - at least one H attached to the carbonyl group
C = O H
C = O H
CH3

4. CARBONYL COMPOUNDS - STRUCTURE
Structure carbonyl groups consists of
a carbon-oxygen double bond
the bond is polar due to the
difference in electronegativity
Difference ALDEHYDES - at least one H attached to the carbonyl group
KETONES - two carbons attached to the carbonyl group
C = O H
C = O H
CH3
C = O
CH3
C = O
C2H5
CH3

5. CARBONYL COMPOUNDS - FORMULAE
Molecular C3H6O
Structural C2H5CHO CH3COCH3
Displayed
Skeletal
C = O H
C2H5
C = O
CH3
H C C C H
H O H
H H
H C C C O
H H H
H H O O

6. CARBONYL COMPOUNDS - NOMENCLATURE
Aldehydes C2H5CHO propanal
Ketones CH3COCH3 propanone
CH3CH2COCH3 butanone
CH3COCH2CH2CH3 pentan-2-one
CH3CH2COCH2CH3 pentan-3-one
C6H5COCH3 phenylethanone

7. CARBONYL COMPOUNDS - FORMATION
ALDEHYDES
Oxidation of
primary (1°) alcohols RCH2OH [O] ——> RCHO H2O
beware of further oxidation RCHO [O] ——> RCOOH
Reduction of
carboxylic acids RCOOH [H] ——> RCHO + H2O

8. CARBONYL COMPOUNDS - FORMATION
ALDEHYDES
Oxidation of
primary (1°) alcohols RCH2OH [O] ——> RCHO H2O
beware of further oxidation RCHO [O] ——> RCOOH
Reduction of
carboxylic acids RCOOH [H] ——> RCHO + H2O
KETONES
secondary (2°) alcohols RCHOHR [O] ——> RCOR H2O
[O] means oxidizing agent like Sodium/potassium dichromate(VI)/potassium
manganate (VII)

9. OXIDATION OF PRIMARY ALCOHOLS
PRIMARY ALCOHOLS OXIDATION TO ALDEHYDES DISTILLATION
 Aldehyde has a lower boiling point so distils off before being oxidised further to get higher yield of Aldehyde

10. OXIDATION OF PRIMARY ALCOHOLS
 If you want to produce carboxylic acid from primary alcohol, heat under reflux and use excess/sufficient oxidizing agent to get higer yield of Carboxylic acid
Reactants = Primary alcohol and excess oxidizing agent

11. OXIDATION OF SECONDARY ALCOHOLS
SECONDARY ALCOHOLS OXIDATION TO CARBOXYLIC ACIDS REFLUX
Note :
volatile compounds
Chemical compounds that transition to gas at low temperatures
Reflux condenser prevents volatile compounds like ethanal, ethanol and ethanoic acid vapours from leaving the flask
Aldehyde condenses back into the mixture and gets oxidised to the acid

12. Why 1° and 2° alcohols are easily oxidised and 3° alcohols are not
OXIDATION OF ALCOHOLS
Why 1° and 2° alcohols are easily oxidised and 3° alcohols are not
For oxidation to take place easily you must have two hydrogen atoms on adjacent C and O atoms.

13. 1° 2° 3° OXIDATION OF ALCOHOLS H H R C O + [O] R C O + H2O H H H H
Why 1° and 2° alcohols are easily oxidised and 3° alcohols are not
For oxidation to take place easily you must have two hydrogen atoms on adjacent C and O atoms.
H H
R C O [O] R C O H2O
H H 1° 2° 3°
H H
R C O [O] R C O H2O
R R
This is possible in 1° and 2° alcohols but not in 3° alcohols.
R H
R C O [O] R

14. PHYSICAL PROPERTIES OF CARBONYL COMPOUNDS
Boiling points
Carbonyl compounds are polar so induced dipole-induced dipole as well as London forces
However, hydrogen bonding is possible between oxygen atoms and carbonyl groups and –OH group in water
Simpler aldehydes such as methanal is freely soluable in water. The simplest keytone, propanone mixes freely with water

15. CARBONYL COMPOUNDS - IDENTIFICATION
Method strong peak around cm-1 in the infra red spectrum
Method formation of an orange precipitate with 2,4-dinitrophenylhydrazine
Although these methods identify a carbonyl group, they cannot tell the difference
between an aldehyde or a ketone. To narrow it down you must do a second test.

16. 2,4-DINITROPHENYLHYDRAZINE
Structure
Use  reacts with carbonyl compounds (aldehydes and ketones)
 used as a simple test for aldehydes and ketones
 makes orange crystalline derivatives - 2,4-
dinitrophenylhydrazones
C6H3(NO2)2NHNH2

19. How would you use the purified product to identify the compound ??
 Measure melting temperature / point
 Compare with literature/database / known value

20. CARBONYL COMPOUNDS - IDENTIFICATION
Differentiation to distinguish aldehydes from ketones, use a mild oxidising
agent
Tollen’s
Reagent ammoniacal silver nitrate
 mild oxidising agent which will oxidise aldehydes to form carboxylic acid
but not oxidise ketones
 contains the diammine silver(I) ion - [Ag(NH3)2 ]+
 the silver(I) ion is reduced to silver Ag+(aq) + e¯ ——> Ag(s)
the test is known as THE SILVER MIRROR TEST

21. Warming To liens' reagent with an aldehyde produces a precipitate of silver which coats clean glass with a shiny layer of silver so that it acts like a mirror (left). There is no reaction with a ketone (right)

22. CARBONYL COMPOUNDS - IDENTIFICATION
Differentiation to distinguish aldehydes from ketones, use a mild oxidising agent
Fehling’s Solution / Benedict’s solution
contains a copper(II) complex ion giving a blue solution
on warming, it will oxidise aldehydes to form carboxylic acid but not
oxidise ketones
the copper(II) is reduced to copper(I)
a red precipitate of copper(I) oxide, Cu2O, is formed
The silver mirror test is the better alternative as it works with all aldehydes
Ketones do not react with Tollen’s Reagent or Fehling’s Solution

23. Fehling's reagent is used to test for aldehydes
Fehling's reagent is used to test for aldehydes. The reagent has a blue colour as it contains copper(II) ions. The test tube in the middle contains Fehling's reagent that has been reduced by an aldehyde, to form an orange-brown precipitate of copper(I) oxide. The test tubes on the left and right contain Fehling's reagent and ketones. Ketones are very similar to aldehydes but do not react with Fehling's reagent, hence the colour is unchanged.

24. TRIIODOMETHANE (IODOFORM) REACTION WITH ALDEHYDES AND KETONES
Triiodomethane (iodoform) reaction can be used to identify the presence of a mythyl group next to carbonyl group
Mythyl group next to carbonyl group
Note:
An alternative reagent for idoform reaction is a mixture of potassium iodide and sodium chlorate(I) solutions

25. CARBONYL COMPOUNDS - CHEMICAL PROPERTIES
OXIDATION
• provides a way of differentiating between aldehydes and ketones
• mild oxidising agents are best
• aldehydes are easier to oxidise
• powerful oxidising agents oxidise ketones to a mixture of carboxylic acids
ALDEHYDES easily oxidised to acids
RCHO(l) [O] ——> RCOOH(l)
CH3CHO(l) [O] ——> CH3COOH(l)
KETONES oxidised under vigorous conditions to acids with fewer carbons
C2H5COCH2CH3(l) [O] ——> C2H5COOH(l) CH3COOH(l)

26. Oxidation by potassium dichromate
Acidified potassium dichromate

27. CARBONYL COMPOUNDS - NUCLEOPHILIC ADDITION
Mechanism occurs with both aldehydes and ketones
involves addition to the C=O double bond
unlike alkenes, they are attacked by nucleophiles
attack is at the positive carbon centre due to the
difference in electronegativities
alkenes are non-polar and are attacked by electrophiles
undergoing electrophilic addition
Group
Bond
Polarity
Attacking species
Result
ALKENES
C=C
NON-POLAR
ELECTROPHILES
ADDITION
CARBONYLS
C=O
POLAR
NUCLEOPHILES
ADDITION

28. CARBONYL COMPOUNDS - NUCLEOPHILIC ADDITION
Reagent hydrogen cyanide - HCN (in the presence of KCN)
Conditions reflux in alkaline solution
Nucleophile cyanide ion CN¯ (Mostly KCN also added with HCN)
Product(s) hydroxynitrile (cyanohydrin)
Equation CH3CHO HCN ——> CH3CH(OH)CN
2-hydroxypropanenitrile
Notes HCN is a weak acid and has difficulty dissociating into ions
HCN H CN¯
the reaction is catalysed by alkali which helps
produce more of the nucleophilic CN¯

29. CARBONYL COMPOUNDS - NUCLEOPHILIC ADDITION
Mechanism Nucleophilic addition
Step 1 CN¯ acts as a nucleophile and attacks the slightly positive C
One of the C=O bonds breaks; a pair of electrons goes onto the O
STEP 1

30. CARBONYL COMPOUNDS - NUCLEOPHILIC ADDITION
Mechanism Nucleophilic addition
Step 1 CN¯ acts as a nucleophile and attacks the slightly positive C
One of the C=O bonds breaks; a pair of electrons goes onto the O
Step 2 A pair of electrons is used to form a bond with H+
Overall, there has been addition of HCN
STEP 1
STEP 2

31. CARBONYL COMPOUNDS - NUCLEOPHILIC ADDITION
Mechanism Nucleophilic addition
Step 1 CN¯ acts as a nucleophile and attacks the slightly positive C
One of the C=O bonds breaks; a pair of electrons goes onto the O
Step 2 A pair of electrons is used to form a bond with H+
Overall, there has been addition of HCN
STEP 1
STEP 2

32. CARBONYL COMPOUNDS - NUCLEOPHILIC ADDITION
Mechanism Nucleophilic addition
Step 1 CN¯ acts as a nucleophile and attacks the slightly positive C
One of the C=O bonds breaks; a pair of electrons goes onto the O
Step 2 A pair of electrons is used to form a bond with H+
Overall, there has been addition of HCN
STEP 1
STEP 2

33. CARBONYL COMPOUNDS - NUCLEOPHILIC ADDITION
ANIMATED MECHANISM

34. Plane polarization of light ??
Light oscillates in many planes (directions) , when light is passed through a Polaroid . It oscillates in only one plane
Light osccilating
in many directions

35. Optical isomerism Optical isomerism is an example of stereo-isomerism.
It occurs when substances have the same molecular and structural formulae, but
one cannot be superimposed on the other. Put simply, they are mirror images of
each other (see the diagram below).
Molecules like this are said to be chiral (pronounced ky-ral), and the different
forms are called enantiomers.
 Optical isomers can occur when there is an asymmetric carbon atom
An asymmetric carbon atom is one which is bonded to four different groups

36. 2 enantiomers / Optical isomers do not superimpose
Does not superimpose

37. CARBONYL COMPOUNDS - NUCLEOPHILIC ADDITION
Watch out for the possibility of optical isomerism in hydroxynitriles
CN¯ attacks from one side
CN¯ attacks from other side

38. CARBONYL COMPOUNDS - NUCLEOPHILIC ADDITION
Watch out for the possibility of optical isomerism in hydroxynitriles
CN¯ attacks
from one side (above)
CN¯ attacks
from other side (below)

39. ANIMATED MECHANISM TO SHOW HOW DIFFERENT ISOMERS ARE FORMED
CARBONYL COMPOUNDS - NUCLEOPHILIC ADDITION
ANIMATED MECHANISM TO SHOW
HOW DIFFERENT ISOMERS ARE FORMED

40. 2 enantiomers  form reacimic mixture
CN¯ attacks from both sides so forms 2 optical isomers / enantiomers which forms a recimic mixture
2 enantiomers  form reacimic mixture

41. How reacimic mixture forms ??
Rotate plane polarized
light to anit clockwise (to the left) and is called the (–) enantiomer.
Rotate plane polarized
light to clockwise (to the right) and is the (+) enantiomer
 A mixture containing equal concentrations of the (+) and (–) enantiomers is not optically active (it will not rotate the plane of polarisation). It is called a racemic mixture or racemate.

42. Optical isomerism and reaction mechanisms
The optical activity of the reactants and products of organic reactions can
help chemists to determine the mechanisms of reactions. This is illustrated
by the outcomes of the SN1 and SN2 mechanisms in nucleophilic substitution reactions.
During the one,step SN2 mechanism, the three groups that remain
attached to the central carbon atom are turned inside out. The molecule is
inverted like an umbrella in a high wind (Figure 6.12).
This means that an optically active halogenoalkane gives rise to an optically active alcohol if substitution takes place by the SN2 mechanism.

43. In the two-step SN2 mechanism, a planar intermediate is formed after the first step. However, attack by the nucleophile during the second step can happen from either side of the planar intermediate. The result is that starting with one optical isomer of a halogenoalkane leads to a product which is a racemic mixture of the two forms of the chiral alcohol. This means that the product is optically inactive (Figure 6.13).

44. The product of this reaction above has a chiral centre
The product of this reaction above has a chiral centre. Would you expect the reaction to produce a solution that rotates the plane of plane-polarized light? Explain your answer.?? No
As:
Reaction site/carbonyl/aldehyde/moecule is planar
Attack (equally likely) from both sides
(gives) racemic mixture

45. CARBONYL COMPOUNDS - REDUCTION WITH NaBH4
Reagent sodium tetrahydridoborate(III) (sodium borohydride), NaBH4
Conditions aqueous or alcoholic solution
Mechanism Nucleophilic addition (also reduction as it is addition of H¯)
Nucleophile H¯ (hydride ion)
Product(s) Alcohols Aldehydes are REDUCED to primary (1°) alcohols.
Ketones are REDUCED to secondary (2°) alcohols.
Equation(s) CH3CHO [H] ——> CH3CH2OH
CH3COCH [H] ——> CH3CHOHCH3
Notes The water provides a proton

46. CARBONYL COMPOUNDS - REDUCTION WITH LiAlH4
 LiAlH4 is a powerful reducing agent which converts aldehydes to primary alcohols and keytones to secondary alcohols. LiAlH4 is easily hydrolized so, reagent is dissolved in dry ether
dry ether

47. CARBONYL COMPOUNDS - REDUCTION WITH HYDROGEN
Reagent hydrogen
Conditions catalyst - nickel or platinum
Reaction type Hydrogenation, reduction
Product(s) Alcohols Aldehydes are REDUCED to primary (1°) alcohols.
Ketones are REDUCED to secondary (2°) alcohols.
Equation(s) CH3CHO H ——> CH3CH2OH
CH3COCH H2 ——> CH3CHOHCH3
Note Hydrogen also reduces C=C bonds
CH2 = CHCHO H ——> CH3CH2CH2OH