OH
Cl
OH
CH 3
OH
CO 2 H
OH
NO 2
NO 2
ortho-Chlorophenol m-Cresol
para-Hydroxybenzoic acid
2,4-Dinitrophenol
1
2
3
4
5
6
Physical properties of phenols
The simplest phenols are liquids or low-melting solids. Because of hydrogen
bonding, phenols have a quite high boiling point (e.g. the boiling point of mcresol is 201
C). Phenol itself is somewhat soluble in water (9 g per 100 g
of water) because of hydrogen bonding with water. Most other phenols are
insoluble in water.
Generally, phenols themselves are colourless. However, they are easily
oxidized to form coloured substances. Phenols are acidic in nature and most
phenols have K a values of $10
À10 .
Physical properties of nitrophenols Physical properties of o-, m- and pnitrophenols differ considerably.
OH
NO 2
OH
NO 2
OH
NO 2
ortho-Nitrophenol
para-Nitrophenol
meta-Nitrophenol
Nitrophenols
Boiling point at 70 mm in
C
Solubility in g/100 g H 2 O
ortho-nitrophenol
100
0.2
meta-nitrophenol
194
1.35
para-nitrophenol
Decomposes
1.69
Among the nitrophenols, meta- and para-nitrophenols have high boiling
points because of intermolecular hydrogen bonding, as shown below.
O
H
N
O
O
O
H
N
O
O
O
H
N
O
O
N
O H
O
O
Intermolecular hydrogen bonding
in ortho-nitrophenol
Intermolecular hydrogen bonding
in meta-nitrophenol
..
:
:
..
..
:
:
..
130
CH4 ORGANIC FUNCTIONAL GROUPS