Crotonic acid
![Ball-and-stick model of the crotonic acid molecule](/Images/godic/202501/07/Crotonic_acid_3D_ball5145.png")
Crotonic acid, or trans-2-butenoic acid, is a short-chain unsaturated carboxylic acid, described by the formula CH3CH=CHCO2H. Crotonic acid is so named because it was erroneously thought to be a saponification product of croton oil. It crystallizes as needles from hot water.