14.0 Physical Properties of Phenol

  Alcohols, Phenols and Ethers

Physical properties of phenols are strongly influenced by hydroxyl group, which permits phenols to form hydrogen bond with other phenol molecule causing high melting and boiling points and also with water causing some (partial) solubility in water. This accounts why phenols have higher melting and boiling points and are more soluble in water than arenes and alkyl halides of comparable molecular weight. Phenol themselves are colourless solid (m.p. 41°C) the colour if any associated with phenols is either due to the presence of some other functional group —NO2 or due to the presence of some oxidized product of phenol as impurity.

Comparative solubility and boiling point is observed in the three isomers (o-m- and p) nitrophenols. p-nitrophenol is capable of forming intermolecular H bond between themselves and with water too, hence it has higher m.p. and more solubility in water m-Nitrophenol also behaves is the same way.

However o-nitrophenol is capable of forming intramolecular H bond. Due to intramolecular H bond neither with its second molecule nor with water. Hence o-nitrophenl has low m.p. and low solublility in water then the corresponding m- and p-isomer.