Q.Define Alcohols and give their classifications.
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Start your 14-day free trial to unlock the full solution →Alcohols are R–OH compounds, and they are classified by how many –OH groups they carry, and by whether the –OH-bearing carbon is primary, secondary or tertiary (or is allylic/benzylic).
Definition: an alcohol is a compound derived formally by replacing one or more hydrogen atoms of an aliphatic hydrocarbon (or of the side chain of an aromatic hydrocarbon) with an equal number of hydroxyl (–OH) groups, where the –OH is bonded to an sp³-hybridised carbon atom (this distinguishes alcohols from phenols, where –OH is on an sp²-hybridised aromatic-ring carbon).
Classification by number of –OH groups:
- Monohydric — one –OH group, e.g. ethanol, CH₃CH₂OH.
- Dihydric — two –OH groups, e.g. ethylene glycol, HOCH₂CH₂OH.
- Trihydric/polyhydric — three or more –OH groups, e.g. glycerol, HOCH₂CH(OH)CH₂OH.
Classification by the type of carbon bearing –OH (for monohydric alcohols):
- Primary (1°) alcohol — the –OH-bearing carbon is attached to only one other carbon (or none), e.g. ethanol.
- Secondary (2°) alcohol — the carbon is attached to two other carbons, e.g. isopropanol, (CH₃)₂CHOH.
- Tertiary (3°) alcohol — the carbon is attached to three other carbons, e.g. tert-butanol, (CH₃)₃COH. …
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