NEET Chemistry Notes Alcohols,Phenols and ethers -Phenols
Aromatic compounds in which hydroxyl group (— OH) is directly attached with benzene nucleus are called phenols.
Some general and important methods of preparation of phenols are discussed below:
Physical Properties of Phenols
Phenol has higher boiling point and soluble in water due to its ability to form hydrogen bond with water.
Acidic Nature of Phenol
Phenols are acidic in nature, even more acidic than alcohols. The more acidic character of phenols (than corresponding aliphatic alcohols) is due to conjugation between lone pair of oxygen and benzene nucleus, i.e.
The positive charge on oxygen signifies the weakening of O—H bond. Presence of electron releasing group like —CH3, —C2H5 over benzene nucleus destabilises the phenoxide ion, thus, decreases the acidity of phenol whereas, presence of electron withdrawing groups like —N02, —CN, etc,, stabilises the phenoxide ion and thus, increases the acidity of phenol.
Chemical Properties of Phenols
Phenols exhibit the following chemical properties.
Electrophilic Substitution Reactions
In phenol, the—OH group shows +R and -I effect and hence, highly activates the benzene ring towards electrophilic substitution reaction. It is ortho and para directing group.
The ortho and para isomers can be separated by steam distillation, o-nitrophenol is steam volatile due to intramolecular hydrogen bonding while p-nitrophenol is less volatile due to intermolecular hydrogen bonding.
Reactions Involving Breaking of O—H Bond
Both the above reactions show acidic nature of phenol.
- Phenol is used in the manufacture of bakelite, soaps, lotions, etc.
- It is used in the manufacture of drugs like aspirin, salol, phenacetin, etc.