Butenoic acid

Butenoic acid is any of three monocarboxylic acids with an unbranched 4-carbon chain with 3 single bonds and one double bond; that is, with the structural formula –––H (2-butenoic) or –––H (3-butenoic). All have the chemical formula or.

These compounds are technically mono-unsaturated fatty acids, although some authors may exclude them for being too short. The three isomers are:
 * crotonic acid (trans-2-butenoic or (2E)-but-2-enoic acid)
 * isocrotonic acid (cis-2-butenoic or (2Z)-but-2-enoic acid)
 * 3-butenoic acid (but-3-enoic acid).