Carboxylic Acids

Carboxylic acids are one of the most widely encountered functional groups in organic chemistry and in everyday life. They contain the carboxyl group (–COOH), which combines a carbonyl (C=O) and a hydroxyl (O–H) in a single functional group. From ethanoic acid in vinegar to citric acid in lemons, carboxylic acids play central roles in biology, industry, and synthesis.

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Structure and Naming

The carboxyl group is written as –COOH or –CO₂H. The carbon of the carboxyl group is always carbon 1 in the naming system, and the suffix -oic acid is used:

• Methanoic acid (HCOOH) — one carbon
• Ethanoic acid (CH₃COOH) — two carbons
• Propanoic acid (CH₃CH₂COOH) — three carbons
• Butanoic acid (CH₃CH₂CH₂COOH) — four carbons

The carboxyl group is always at the end of the chain, so no positional number is needed for it.

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Physical Properties and Hydrogen Bonding