A carboxylic acid is an organic compound containing a carboxyl group. This structure has a carbon atom having a double-bonded oxygen atom and a hydroxyl group bonded to it, with one space left over to bind to the rest of the molecule. The general formula for a carboxylic acid is R-COOH. Carboxylic acids containing fewer than five carbon atoms are water-soluble, and when they dissolve, the hydroxyl group yields its proton to a water molecule; the result is a hydronium ion and a monovalent organic anion called a carboxylate ion. The formula now is R-COO-, and its structure undergoes a key change: instead of having one double-bonded oxygen and one single-bonded oxygen, the carbon atom and the two oxygen atoms form a resonance structure.
A carboxylic acid might be liquid at 25 degrees Celsius, in which case its pure form is often called the glacial form. The pure form of the acid is named by adding the suffix -anoic to the numeric infix and following this word with the word acid--hence, methanoic acid, ethanoic acid, propanoic acid, butanoic acid, pentanoic acid, and so forth. The name of the dissociated, or anionic, form has the terminal -ic syllable changed to -ate. (Note: the first four carboxylic acids have the traditional names formic acid, acetic acid, propionic acid, butyric acid.[note 1])
The condensation reaction between a carboxylic acid and an alcohol forms an ester compound.
- There are also traditional names for carboxylic acids with 5 atoms (valeric acid) and 6 atoms (caproic acid)
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