Caffeic acid
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![In plants, caffeic acid (middle) is formed from 4-hydroxycinnamic acid (left) and is transformed to ferulic acid.](/Images/godic/202501/02/CaffeicAcIn5620.png")
Caffeic acid is an organic compound that is classified as hydroxycinnamic acid. This yellow solid consists of both phenolic and acrylic functional groups. It is found in all plants because it is a key intermediate in the biosynthesis of lignin, one of the principal components of plant biomass and its residues.