This topic accounts for approximately 5% of your exam marks.
stable
Rare
Stable5%
Properties and reactions with carbonates and alcohols tested as shorter questions.
What a carboxylic acid is
Carboxylic acids are a homologous series of organic compounds containing the carboxyl functional group, −COOH
The carboxyl group is what makes these compounds acidic — it is the proton-donor end of the molecule (compare with acids in topic 16)
Common examples include vinegar (an aqueous solution of ethanoic acid, about 5% by volume), the methanoic acid in nettle stings, and the long-chain fatty acids that make up animal and plant fats
The carboxyl group up close
The −COOH group consists of:
A central carbon
A C=O double bond to one oxygen
A single bond to a separate O−H group
The whole group is written as −COOH for short, or drawn out as −C(=O)−O−H when every bond is shown
The hydrogen of the O−H is the acidic hydrogen — it is the proton released into solution that gives a carboxylic acid its acid character
General formula
The general formula of the carboxylic acid series is:
CnH2n+1COOH
where n counts only the carbons sitting in the alkyl chain bonded to the −COOH group — it does not count the carbon already inside the carboxyl group itself
A molecule with n alkyl carbons therefore has (n + 1) carbon atoms in total, including the one in the −COOH
Special case: when n = 0, the alkyl chain is just a single hydrogen atom and the formula reduces to HCOOH (methanoic acid). This is the smallest member of the series
Naming carboxylic acids
The name follows the standard stem-plus-ending convention from topic 21, with the ending "-anoic acid":