Nomenclature

Full Notes

Nomenclature of Alcohols

The common name of an alcohol is based on the alkyl group and the word alcohol.

Examples:

• CH₃OH = Methyl alcohol
• CH₃CH₂OH = Ethyl alcohol
• CH₃C(CH₃)OHCH₃ = Tert-butyl alcohol

IUPAC System:

1. Select the longest continuous chain of carbon atoms containing the –OH group.
2. Replace the final ‘e’ in the corresponding alkane with –ol.
3. Number the chain so that the carbon attached to –OH gets the lowest possible number.
4. If necessary, indicate the position of the –OH group and any substituents.

Examples:

• CH₃CH₂CH(OH)CH₃ = Butan-2-ol
• CH₃CH₂CH₂CH₂OH = Butan-1-ol

Cyclic alcohols:

Cyclic alcohols are named with the prefix ‘cyclo’, and the carbon atom bonded to the –OH group is always given position number 1 in the ring.

Nomenclature of Phenols

Phenols are named as derivatives of phenol.

• Substituents on the benzene ring are numbered such that the –OH group is assigned position 1.
• Prefixes are used to denote the position and type of substituent.

Examples:

• C₆H₅OH = Phenol
• 2-CH₃–C₆H₄OH = o-Cresol (or 2-methylphenol)
• 3-CH₃–C₆H₄OH = m-Cresol (or 3-methylphenol)

Nomenclature of Ethers

Common System:
Names are given by listing alkyl groups alphabetically followed by the word “ether”.

Examples:

• CH₃CH₂OCH₂CH₃ = Diethyl ether

• CH₃OC₂H₅ = Ethyl methyl ether

IUPAC System:

1. Consider the ether as an alkoxy-substituted alkane.
2. The shorter alkyl group becomes the alkoxy prefix (e.g., methoxy, ethoxy).
3. The longer chain is the parent hydrocarbon.
4. Number the chain from the end nearest to the –O– group.

Examples:

• CH₃OCH₂CH₃ → Methoxyethane
• CH₃CH₂CH₂OCH₃ → 1-Methoxypropane
• C₆H₅OCH₃ → Methoxybenzene (common name: Anisole)

Naming Examples

Summary

• Alcohols use the suffix –ol and are numbered from the carbon closest to the –OH group.
• Phenols are named as substituted derivatives of phenol with the –OH at position 1.
• Ethers are named as alkoxyalkanes using the shorter chain as the alkoxy prefix.
• Common names for alcohols and ethers are still widely used in practice.