THE CHEMISTRY
OF ALDEHYDES AND
KETONES
By
Dr. Nahed Nasser
ALDEHYDES & KETONES
CONTENTS
• Bonding in carbonyl compounds
• Structural differences between aldehydes and ketones
• Drawing aldehydes and ketones
• Nomenclature of aldehydes and ketones
• Physical properties of aldehydes and ketones
•Preparation of aldehydes and ketones
•Reactions of adehydes and ketones
CARBONYL COMPOUNDS
Carbonyl compounds contain CO group, they include aldehydes, ketones, acids and
acid derivatives
Bonding
the carbon is sp2 hybridised and formsthree sigma (s) bonds
the unhybridised 2p orbital of carbon is overlaps with a 2p orbital of
oxygen to form a pi (p) bond
P –ORBITALS
PLANAR
WITH
BOND
ANGLES
OF 120°
ORBITAL
OVERLAP
as oxygen is more electronegative than carbon the bond is polarized
The implications of these effects are:
higher melting and boiling points compared to analogous alkanes
lower boiling points than analogous alcohols
more soluble than alkanes but less soluble than alcohols in aqueous media
NEW
ORBITAL
Structural differences between aldehydes
and ketones
Aldehydes and ketones contains the same functional group, the carbonyl group (> C = O).
Difference
ALDEHYDES (RCHO) - at least one H attached to the carbonyl
group thus the aldehydic group (CHO) is always terminal
CH3
H
C=O
C=O
H
H
KETONES RCOR’ (R and R’=alkyl or aryl )- two carbons attached to
the carbonyl group
C2H5
CH3
C=O
CH3
C=O
CH3
Drawing aldehydes and ketones
Molecular Formula
C 3H 6O
Structural Formula
C2H5CHO
CH3COCH3
CH3
C2H5
C=O
C=O
H
CH3
O
H
Bond line formula
O
O
5
NOMENCLATURE Of CARBONYL COMPOUNDS
IUPAC Nomenclature of Aldehydes:
• Find the longest continuous carbon chain contains the CHO group to
get the name of the parent hydrocarbon, the ending e is then replaced by
the suffix –al.
O
H
C
O
O
H
H3C
H3C CH2 C
H
O
H
H3CH 2CH 2C
C
H
IUPAC:
Methanal
Ethanal
Propanal
Butanal
Common: Formaldehyde Acetaldehyde Propionaldehyde
Butyraldehyde
• The CHO group is assigned the number 1 position and takes precedence
over other functional groups that may the present such as –OH, C=C, OR,
Cl
O
O
C=O, for example:
H
IUPAC:
HO
3-Chlorobutanal
Common  -Chlorobutyraldehyde
H
3-Hydroxypropanal
 -Hydroxypropionaldehyde
O
2-Butenal
• Aromatic aldehydes are usually designated as derivatives of the
simplest aromatic aldehyde, Benzaldehyde.
O
O
H
OH
Commnon:
4-Nitrobenzaldehyde
H
H
H
H3CO
O 2N
IUPAC: Benzaldehyde
O
O
2-Hydroxybenzaldehyde
Salicylaldehyde
4-Methoxybenzaldehyde
Anisaldehyde
7
Nomenclature of Ketones
•
Common names: derived by listing the alkyl substitutents attached to the carbonyl
group in alphabetical order, followed by the word ketone.
•
IUPAC names: derived from the parent hydrocarbon and relpacing the ending –e by
the suffix –one. The chain is numbred in such a way as give the lowest number to the
C=O group.
O
H3C
C
O
CH3
IUPAC:
Propanone
Common: Dimethyl ketone
Acetone
O
H3C
C C6 H 5
Phenyl ethanone
Methyl phenyl ketone
Acetophenone
H3C
C2 H 5
C CH=CH 2 H5C6
C
C6H5
3-Buten-2-one
Diphenylmethanone
Methyl vinyl ketone
O
O
O
Diphenyl ketone
Benzophenone
O
OH
CHO
C
C2 H 5
IUPAC:
Cyclopentylpropanone
3-Ethyl-2-hydroxycyclohexanone
5-Oxohexanal
PHYSICAL PROPERTIES OF KETONES AND
ALDEHYDE
• Because the polarity of the carbonyl group, aldehydes and
ketones are polar compounds.


O
C
+
O
C
O
-
C




C
O

• Dipole-dipole attractions, although important, are not as
strong as interactions due to hydrogen bonding. As a result,
the boiling points of aldehydes and ketones are higher
than those of non polar alkanes, but lower than those of
alcohols.

C

O


H
O


H


O
C
• The lower aldehydes and ketones are more soluble than
alkanes but less soluble than alcohols in aqueous media
Preparation of aldehydes and ketones
1- Oxidation of alcohols
RCH 2
OH
CrO 3/ pyridine
O
R
Cu / heat
H
O
CrO 3/ pyridine
R2CH
R
OH
C
R
Cu / heat
2- Ozonolysis of alkenes
i) O3
ii) Zn / H2O
CH3CH2CHO + CH3CHO
two aldehydes
O
i) O3
ii) Zn / H2O
O
Diketone
3- Hydration of alkynes
H
C
C
+
HO H
H2SO4, HgSO 4
H
C
C
OH
an enol unstable
O
O
AlCl3
R
Cl
N.B: -COR group is m-director
C
H
O
carbonyl more stable
4- Friedel Crafts acylation
+
C
R
• Typical aldehydes and ketones
Reactions
Reduction (formation of alcohols)
Nucleophilic addition reactions:
1-Addition of HCN
2- Addition of acetylide anion
3-Addtion of alcohols
4-Addition of ammonia and ammonia derivatives
5- Oxidation reactions
a) By K2Cr2O7 or KMnO4
b) By Iodoform reaction
12
REACTIONS OF ALDEHYDES AND
KETONES
1- Reduction : formation of alcohols
Catalytic hydrogenation
/H
2- By nucleophilic addition of Grignard reagent to
aldehydes and ketones (formation of alcohols)
• Addition of RMgX to formaldehyde gives 1◦ alc.
• Addition of RMgX to any other aldehyde gives 2◦ alc.
• Addition of RMgX to ketones gives 3◦ alc.
O
OH
H
+ RMgX
H
1) Dry ether
2) H2O
H
H
R
1° alcohol
R'
O
R
+
C
R'MgX
H
1) Dry ether
R
+
C
OH
HO
O
H3C
CH
2) H 2O
C2H5MgX
H
1) Dry ether
2) H 2O
H3C
CH
C2H5
R'
O
R
C
R'
+
R''MgX
1) Dry ether
2) H 2O
R
C
OH
R''
CH3
O
+
CH 3MgX
1) Dry ether
2) H 2O
OH
3- Addition of Hydrogen Cyanide: Formation of cynohydrins
R'
O
R
C
+
R'
R
HCN
C
OH
CN
Cyanohydrin
CN
O
H
NH2
OH
+
OH
H2 / Pt
+
or LiAlH 4 and H 3O
HCN
Benzaldehyde cyanohydrin
O
OH
+
CN
HCN
H3O
OH
+
COOH
Heat
4- Addition of alkynide ions:
R'
O
R
C
R'
+
-
2
C Na
R C
H3 O
+
+
R
C
C
C
R
OH
O
+ H3C
C
-
C Na
+
H3O
+
OH
C
C
CH3
2
5- Addition of alcohols:
R'O
O
R
C
2
R =H:
2
R =Alkyl
+
2
R'OH
H
R
R''OH
C
OH
R
Hemiacetal
Ketone
Hemiketal
+
C2H5OH
H3C
C
H 5C 2O
CH
OC 2H5
CH3
C2H5OH
C2H5OH
+
H
H3C
C
OC 2H5
H5C2O
H
H3C
CH
Acetal
HO
+
+
2
Ketal
Hemiacetal
H3C
OR''
R
Acetal
H
H
O
C
HO
+
C
R
+
H
2
R
Aldehyde
O
H3C
R'O
+
OC 2H5
CH3
Hemiketal
C2H5OH
+
H
H3C
C
CH3
Ketal
OC 2H5
6- Addition of Ammonia and Ammonia Derivatives
NH3
C
NH
Imine
NH 2OH
Hydroxylamine
H2N
C N OH
Oxime
NH2
C
Hydrazine
C
N
NH2
Hydrazone
O
H2N
NH
C
Phenylhydrazine
NO 2
O 2N
NO 2
NH
C
NH C
Semicarbazide
NH
N
-
O
H2N
NH
Phenylhydrazone
O 2N
H2N
N
NH2
2,4 Dinitrophenylhydrazone
O
C
N
NH
C
Semicarbazone
NH2
3- Oxidation reactions
a)By KMnO4 or K2Cr2O7:
Only aldehydes can be oxidized ketones resist oxidation
R-CHO or
Ar-CHO
KMnO4
or
RCOOH
or K Cr O
2 2 7
ArCOOH
b) Iodoform reaction:
• This reaction gives positive result with any aldehyde or ketone has a
methyl ketone group (CH3CO) , therefore acetaldehyde is the only
aldehyde gives positive iodoform test.
O
H3C
C O
+
3 I2
+
4 NaOH
R
O Na
R
CH3
H3C
O
-
I2 / NaOH
H3C
18
COONa
+
+ CHI3 +
+
CHI3
3 NaI