Carboxylic Acids

Carboxylic acids contain the carboxyl group, COOH. The carbon of this group has a C=O double bond and is also bonded to an OH group. Their general formula is RCOOH; for the aliphatic acids this is C_nH_2n+1COOH.Naming: take the name of the alkane with the same total number of carbon atoms, drop the final 'e' and add '-oic acid'. The carboxyl carbon is always carbon 1, so it never needs a number.
• HCOOH: methanoic acid
• CH₃COOH: ethanoic acid
• CH₃CH₂COOH: propanoic acid
• C₆H₅COOH: benzoic acid
An acid with a COOH group at each end is a dicarboxylic acid; for example HOOCCOOH is ethanedioic acid.Acidity: carboxylic acids are weak acids. They only partially dissociate in water, releasing H⁺ ions and forming carboxylate ions:CH₃COOH ⇌ CH₃COO⁻ + H⁺The position of equilibrium lies well to the left. The carboxylate ion is stabilised because its negative charge is delocalised over both oxygen atoms. Carboxylic acids are stronger acids than alcohols and phenol, but much weaker than strong acids such as hydrochloric acid.Worked example: name (CH₃)₂CHCOOH. The longest chain that includes the COOH carbon has 3 carbons (propanoic acid), and there is a methyl branch on carbon 2, so the name is 2-methylpropanoic acid.