Classification of carboxylic acids

Carboxylic acids are classified as aliphatic or aromatic. ALIPHATIC CARBOXYLIC ACIDS (also called fatty acids) have the -COOH (carboxyl) group bonded to an alkyl group; general formula R-COOH, R = H or alkyl. As with formaldehyde among the aldehydes, there is one exception: formic acid, H-COOH, is still classed as an aliphatic carboxylic acid even though its -COOH is not attached to any carbon at all. Worked examples: acetic acid (CH3-COOH) and propionic acid (CH3-CH2-COOH), both MONOcarboxylic acids (one -COOH group); oxalic acid (HOOC-COOH), a DIcarboxylic acid (two -COOH groups bonded directly to each other); and citric acid (a central carbon bearing an -OH plus three -COOH-bearing arms), a TRIcarboxylic acid. Carboxylic acids are widely distributed in nature, in both plants and animals: L-lactic acid occurs in curd, citric acid in citrus fruit such as lemons, and acetic acid is the key ingredient of vinegar. AROMATIC CARBOXYLIC ACIDS have one or more -COOH groups attached DIRECTLY to the aromatic ring -- e.g. benzoic acid (one ring -COOH) and phthalic acid (two ring -COOH groups, at adjacent/ortho positions, i.e. benzene-1,2-dicarboxylic acid); aspirin (acetyl salicylic acid) is a further example, carrying a ring -COOH plus a ring -OCOCH3 ester group. A 'Remember' box draws an important distinction: if the -COOH group is NOT attached directly to the ring -- e.g. phenylacetic acid, C6H5-C …