Download The carbonyl group

The carbonyl group
• The carbonyl group (C=O) is found in
aldehydes, ketones, and many other organic
functional groups.
• In ketones, two carbon groups are attached
to the carbonyl carbon.
• While in aldehydes at least one hydrogen is
attached to the carbon.
Aliphatic
formaldehyde
Aldehydes
Aromatic
Benzaldehyde
Acetone
Ketones
Aliphatic
Aromatic
Acetophenone
Physical properties
• The carbonyl group is a strong dipole. This
causes the B.P of aldehydes and ketones to be
higher than similar molecular weight alkanes
and others but lower than alcohols which are
held together by H-bonds.
Aldehyde < Alcohols > Alkane
Solubility
• Because aldehydes have an O atom, they can
H-Bond with water. They are about as soluble
in water as alcohols of comparable weight.
Chemical Properties
1. 2,4 Dinitrophenyl hydrazine test
• Aldehydes and ketones react with a number of
nitrogen containing compounds through
nucleophilic addition and subsequent loss of
water to give products that have a carbon
nitrogen double bond. These reactions are
useful in distinguishing an aldehyde or ketone
from other functional groups. (General test)
NO2
NO2
R
+
C O +H2N NH
R
aldehyde
or ketone
2,4
NO2
dinitrophenylhydrazine
+ve result yellow ppt
H
R
C N NH
R
2,4 dinitrophenylhydrazone
NO2
2. Tollen’s test
• Aldehydes are very easily oxidized to yield
carboxylic acids or their salts if the reaction is
done in basic media.
• This test is a useful method of differentiating
between aldehydes and ketones.
• The silver ion is reduced to metallic silver in a
positive reaction.
RCHO + 2Ag(NH3)2OH
2Ag(s) + RCOO-NH4+ + H2O + NH3
3. Fehling’s test
• To distinguish aliphatic from aromatic
aldehydes.
O
R C H + 2Cu+2 + 5 HOBlue solution
O
R C O- + Cu+2
Red ppt
4. Iodoform test
• Ketones can be distinguish by their reaction
with iodine in a basic solution to yield
iodoform as a yellow colored ppt.