Carbonyl Compounds
Ketones and aldehydes contain the
carbonyl functional group, C=O.
Formation of the C=O carbonyl π bond
π bond formed by sideways overlap of p
orbitals above and below the plane of the
molecule. The bonding electrons are drawn
towards the more electronegative oxygen atom.
p orbitals overlap
C O
δ+
C
O
δ-
Electrons drawn
towards the
more
electronegative
oxygen atom,
creating a dipole
in the C=O bond.
Physical Properties of Carbonyl Compounds
Compound
Intermolecular
forces present
Boiling
Point
Aldehyde
Dipole-Dipole
21
Alcohol
Dipole-Dipole
Hydrogen bonds
79
Carboxylic
Acid
Dipole-Dipole
Hydrogen Bonds
118
Aldehydes have a lower boiling point than the
comparable alcohol or carboxylic acid. They have dipole
dipole forces, which are weaker than the hydrogen
bonds present in alcohols and carboxylic acids.
Uses of aldehydes (methanal): manufacturing plastic
coating such as formica; preserving and embalming; feedstock
in pharmaceuticals, perfumes and flavouring agents.
Uses of ketones (propanone): solvents – like nail varnish
removed, in paints and varnishes.
Miscibility with Water:
The polarity of carbonyl compounds is sufficient
to enable the lower members of the homologous
series to be completely miscible with water.
Water will form hydrogen bonds to the carbonyl
group. Aldehydes and ketones with more than 4
carbon atoms become increasingly immiscible in
water because the hydrocarbon chain is
hydrophobic – it hinders the formation of
hydrogen bonds between the lone pair of
electrons on the oxygen atom of carbonyl group
and water molecules.
𝜹
..
𝜹
𝜹
𝜹
−
+
+
−
Reduction reaction of carbonyl compounds
Reduction reactions of carbonyl compounds form alcohols.
+ 2[H]
Propanal
+
2[H]
NaBH4 (sodium borohydride)
in the presence of water

Propan-1-ol
This reaction
occurs by a
nucleophilic
addition
mechanism
 The lone pair of electrons from the :Hnucleophile attack the electron deficient
carbon atom of the carbonyl functional
group forming a dative covalent bond.
 At the same time, the π bond in the C=O
bond breaks to produce a negatively
charged intermediate. Both π electrons
are on the oxygen atom
 The intermediate ion rapidly reacts with
a hydrogen atom of a water molecule
 The organic product formed is an alcohol.
Characteristic Tests for Carbonyl Compounds
1. Identifying a carbonyl compound
 Add 2,4-dinitrophenylhydrazine (2,4-DNPH)
 Bright orange-yellow crystals will form if the
compound in an aldehyde or ketone
 Filter the precipitate and purify by recrystallisation
 Measure the melting point of dry crystals
 Compare the known melting point from data bases to
identify the actual carbonyl compound
2. Aldehyde or Ketone?
 Add warm Tollen’s Reagent
 Only aldehydes will give a positive test
result: if an aldehyde is present, a ‘silver
mirror’ will form
Ag+ (aq) + e-  Ag (s)
Tollen’s Reagent is
ammoniacal silver nitrate.
It is a mild oxidising agent
containing the complex ion
[Ag(NH3)2]+ . If an
aldehyde is present, it will
be oxidised to a
carboxylic acid, and the
Ag+ in the Tollen’s reagent
will be reduced to Ag.
This is what forms the
‘silver mirror’.