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Alcohols, Phenols and Ethers - Classification and Nomenclature

Grade 12CBSEChemistry

Review the key concepts, formulae, and examples before starting your quiz.

🔑Concepts

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Alcohols are classified as monohydric, dihydric, trihydric, or polyhydric depending on whether they contain one, two, three, or many hydroxyl (−OH-OH) groups in their structures.

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Alcohols are further classified based on the hybridization of the carbon atom to which the −OH-OH group is attached. sp3sp^3 C−OHC-OH alcohols include Primary (1∘1^\circ), Secondary (2∘2^\circ), and Tertiary (3∘3^\circ) alcohols.

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Allylic alcohols contain the −OH-OH group attached to an sp3sp^3 hybridized carbon atom next to a carbon-carbon double bond (e.g., CH2=CH−CH2OHCH_2=CH-CH_2OH).

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Benzylic alcohols have the −OH-OH group attached to an sp3sp^3 hybridized carbon atom next to an aromatic ring (e.g., C6H5CH2OHC_6H_5CH_2OH).

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Phenols are compounds where the −OH-OH group is directly bonded to the sp2sp^2 hybridized carbon atom of an aromatic ring.

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Ethers are classified as Symmetrical (Simple) if the two alkyl or aryl groups attached to the oxygen atom are the same (R−O−RR-O-R), and Unsymmetrical (Mixed) if the groups are different (R−O−R′R-O-R').

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According to IUPAC nomenclature, alcohols are named by replacing the 'e' of the parent alkane with the suffix '-ol'. The position of the −OH-OH group is indicated by a number.

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Ethers are named as 'alkoxyalkanes' in the IUPAC system, where the smaller alkyl group is taken as part of the alkoxy group and the larger group forms the parent alkane chain.

📐Formulae

CnH2n+1OHC_n H_{2n+1} OH

R−O−R′R-O-R'

C6H5OHC_6H_5OH

CH2(OH)−CH(OH)−CH2(OH)CH_2(OH)-CH(OH)-CH_2(OH)

💡Examples

Problem 1:

Write the IUPAC name of the following compound: CH3−CH(CH3)−CH(OH)−CH3CH_3-CH(CH_3)-CH(OH)-CH_3.

Solution:

3-Methylbutan-2-ol

Explanation:

The longest carbon chain containing the −OH-OH group has 4 carbons (butane). Numbering starts from the right to give the −OH-OH group the lowest possible locant (2). A methyl substituent is present at the 3rd carbon.

Problem 2:

Give the IUPAC name for CH3−O−CH2−CH2−CH3CH_3-O-CH_2-CH_2-CH_3.

Solution:

1-Methoxypropane

Explanation:

This is an unsymmetrical ether. The smaller alkyl group is CH3CH_3 (methoxy) and the longer chain is propane. The methoxy group is attached to the first carbon of the propane chain.

Problem 3:

Classify the following as 1∘,2∘1^\circ, 2^\circ or 3∘3^\circ alcohol: (CH3)3C−OH(CH_3)_3C-OH.

Solution:

Tertiary (3∘3^\circ) alcohol

Explanation:

The hydroxyl group (−OH-OH) is attached to a carbon atom that is further bonded to three other carbon atoms (three methyl groups).

Problem 4:

Write the IUPAC name of oo-cresol.

Solution:

2-Methylphenol

Explanation:

In oo-cresol, a methyl group (−CH3-CH_3) is present at the ortho position (carbon 2) relative to the hydroxyl group (−OH-OH) on the benzene ring.