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Naming Carboxylic Acids

(Chemical) Definition of Carboxylic Acids:

Carboxylic Acids are organic chemical compounds that include:

  • a -carbonyl group (i.e. an oxygen atom attached to a carbon atom by a double covalent bond)
  • a -hydroxyl group (i.e. an oxygen atom attached to a carbon atom by a single covalent bond and a hydrogen attached to the same oxygen atom by another single covalent bond)
    ... both attached to the same carbon atom.

Due to carbon having a valancy of 4, the carbon atom to which these two functional groups are attached must always be located at the end of a chain of carbon atoms, the length of the chain varying from one (carbon atom) upwards:

Carboxylic Acid - Functional Group


Carboxylic Acid molecules can vary in size up to very long molecules most of which consist of carbon atoms attached to each other and also to hydrogen atoms.

Names of Carboxylic Acids in General

Carboxylic Acids are named according to the same system as other organic compounds, with the suffix -oic acid used to indicate that both a carbonyl group and a hydroxyl group are both attached to the same carbon atom, which is located at the end of a chain or branch of carbon atoms forming the molecule (except in the case of methanoic acid, which includes only one carbon atom).


The first step to consider when working out the name of a carboxylic acid molecule is the number of carbon atoms forming a chain. If they are attached together in a linear (i.e. unbranched) configuration then the number of carbon atoms is indicated according to the same system as used for naming alkanes.

However, if the carbon atoms do not form a simple linear chain, but include branches, the longest linear chain of carbon atoms within the molecule determines the base of the name of the compound, onto which is added information about the branches incl. their lengths in terms of the number of carbon atoms in each branch (i.e. methyl- usually indicates a branch consisting of just one carbon atom attached to the main chain, ethyl- indicates a branch of two carbon atoms in length, etc.) and their positions along the longest linear carbon chain (e.g. attached to the 2nd carbon, 3rd carbon, etc.).

The simplest linear caboxylic acids are named and their structures drawn in the following table.
More complex alcohol molecules follow afterwards.

Names and Structures of simple Linear Carboxylic Acids

The first ten members of the homologous series of linear carboxylic acids are represented below. (The simple structures drawn below show bond types such as single and double bonds, but not accurate bond angles.)

Simple Structure

Other Names = Synonyns
(*Examples not complete lists)

and simple formula

showing bond types but not accurate bond angles


methanoic acid (CH2O2)

Structure of methanoic acid


ethanoic acid (C2H4O2)

Structure of ethanoic acid


propanoic acid (C3H6O2)

Structure of propanoic acid


butanoic acid (C4H8O2)

Structure of butanoic acid


pentanoic acid (C5H10O2)

Structure of pentanoic acid


hexanoic acid (C6H12O2)

Structure of hexanoic acid


heptanoic acid (C7H14O2)

Structure of heptanoic acid


octanoic acid (C8H16O2)

Structure of octanoic acid


nonanoic acid (C9H18O2)

Structure of nonanoic acid


decanoic acid (C10H20O2)

Structure of decanoic acid

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