Classification of Alcohols and Phenols

− Classification of Alcohols
On the basis of type of chain

Aliphatic alcohols

When the hydroxyl group (-OH group) of an alcohol is attached to an aliphatic carbon chain (open chain), the alcohol is called an aliphatic alcohol.


Aliphatic alcohol : methanol


Butane-2,3-diol is an example of an aliphatic alcohol

Aromatic alcohols

When the hydroxyl group is attached to the carbon chain which is attached to an aromatic ring, the alcohol is known as aromatic alcohol.


Aromatic alcohol : phenylmethanol


Aromatic alcohol example : 2-phenylethanol

−Classification of Alcohols
On the basis of number of hydroxyl groups present

Monohydric, dihydric, trihydric and polyhydric alcohols contain 1, 2, 3 and many alcohols respectively.

Dihydric alcohol

ethane-1,2-diol is a dihydric alcohol

Trihydric alcohol

Classification of alcohols : Trihydric alcohol

Monohydric alcohol

Methanol is an example of a monohydric alcohol

Polyhydric alcohol

Classification of alcohols : Polyhydric alcohol

−Classification of Alocohols
As primary, secondary and tertiary alcohols

If the hydroxyl group is attached to a primary carbon, it is called primary alcohol. Similarly, secondary and tertiary alcohols are attached to secondary and tertiary carbons respectively.

Primary alcohol (1°)

Primary alcohol example : Ethanol

Secondary alcohol (2°)

Secondary alcohol example : Propan-2-ol

Tertiary alcohol (3°)

Tertiary alcohol example : 2-Methyl-propan-2-ol

Classification of Phenols

Phenols are classified as monohydric, dihydric, trihydric, polyhydric etc.


Monohydric phenol example : Phenol


Dihydric phenol example : Benzene-1,2-diol


Trihydric phenol example : Benzene-1,3,5-triol


Question : Classify the following as primary, secondary and tertiary alcohols

  1. (CH3)3CCH2OH
  2. CH2=CHCH2OH
  3. C6H5CH(OH)CH3
  4. (CH3)3COH

Answer : The answer is written in the following table :

(CH3)3CCH2OHPrimary alcohol
CH2=CHCH2OHPrimary alcohol
C6H5CH(OH)CH3Secondary alcohol
(CH3)3COHTertiary alcohol