Based on the number of hydroxyl groups connected, alcohols can be classified into three types.
Monohydric alcohols:
They contain one -OH group. Example, CH3CH2-OH
Dihydric alcohols:
They contain two -OH groups. Example 1,2-Ethanol.
Trihydric alcohols:
They contain three -OH groups. Example 1,2,3-Propantriol.
Depending on the number of carbon atoms directly connected to the carbon bonded with the -OH group, alcohols can be distinguished into three types.
Primary alcohols: One carbon atom is directly attached.
Secondary alcohols: Two carbon atoms are directly attached.
Tertiary alcohol: Three carbon atoms are directly attached.
Allylic alcohols:
The -OH groups are attached to an sp3 hybridized carbon next to the c-c double bond in these alcohols.
Benzylic alcohols:
The OH group is attached to a benzylic carbon atom in these alcohols.
Compounds containing Csp2-OH bond
These alcohol contain an OH group bonded to a carbon-carbon double bond, i.e., vinylic carbon or aryl carbon. Ex vinylic alcohol.
Students may refer to the CBSE Class 12 Chemistry Chapter 11 study materials at the Extramarks website.
Classification of Phenol:
As stated in the Chemistry Class 12 Chapter 11 Notes, Phenols can be classified in three ways based on the number of hydroxyl groups attached.
Monohydric phenols:
They contain one -OH group.
Dihydric phenols:
They contain two -OH groups. They may be ortho-, meta- or para- derivatives.
Trihydric phenols:
They contain three -OH groups.
Classification of Alcohol, Phenol, and Ether:
Alcohol Classification:
Alcohols are categorized based on the number of -OH groups and the carbon atoms directly attached to the carbon bonded with the -OH group. They are divided into monohydric, dihydric, and trihydric alcohols. Additionally, they are classified as primary, secondary, or tertiary based on the number of carbon atoms directly attached.
Phenol Classification:
Phenols are classified according to the number of -OH groups they contain, which can be monohydric, dihydric, or trihydric. Dihydric phenols further differentiate into ortho-, meta-, or para- derivatives.
Ether Classification:
Ethers are grouped based on the types of alkyl or aryl groups attached to the oxygen atom. They are classified as symmetrical or unsymmetrical depending on whether the groups on either side of the oxygen are identical.
Nomenclature:
Naming conventions for alcohols, phenols, and ethers follow IUPAC guidelines or common naming practices. They derive their names from the alkyl or aryl groups present, with appropriate suffixes indicating their functional groups.
Preparation:
Alcohols can be prepared through various methods including hydrolysis of halides, hydration of alkenes, reduction of aldehydes, ketones, or carboxylic acids, hydroboration of alkenes, and Grignard synthesis. Phenols are synthesized from sulfonic acids, diazonium salts, or cumene. Ethers are obtained through intermolecular dehydration of alcohols or Williamson synthesis.
Physical Properties:
Alcohols and phenols exhibit water solubility due to hydrogen bonding and possess polar and protic properties. Ethers, on the other hand, have lower boiling points compared to alcohols and can form hydrogen bonds with water.
Chemical Reactions:
Alcohols and phenols undergo a variety of chemical reactions such as reaction with metals, esterification, reaction with hydrogen halides, dehydration, and oxidation. Phenols demonstrate unique reactions including halogenation, nitration, Reimer-Tiemann reaction, Kolbe’s reaction, and oxidation to benzoquinone. Ethers, although less reactive, can undergo cleavage of C-O bonds and electrophilic substitution reactions.