Crotonic acid ((2E)-but-2-enoic acid) or is a short-chain unsaturated carboxylic acid, described by the formula CH3CH=CHCO2H. It is called crotonic acid because it was erroneously thought to be a saponification product of croton oil. It crystallizes as colorless needles from hot water. The cis-isomer of crotonic acid is called isocrotonic acid. Crotonic acid is soluble in water and many organic solvents. Its odor is similar to butyric acid. Crotonic acid ((2E)-but-2-enoic acid) or is a short-chain unsaturated carboxylic acid, described by the formula CH3CH=CHCO2H. It is called crotonic acid because it was erroneously thought to be a saponification product of croton oil. It crystallizes as colorless needles from hot water. The cis-isomer of crotonic acid is called isocrotonic acid. Crotonic acid is soluble in water and many organic solvents. Its odor is similar to butyric acid.