Truxillic acid


Truxillic acids are any of several crystalline stereoisomeric cyclic dicarboxylic acids with the formula 2. They are colorless solids. These compounds are obtained by the Woodward-Hoffmann rules| photocycloadditions of cinnamic acid where the two trans alkenes react head-to-tail. The isolated stereoisomers are called truxillic acids. The preparation of truxillic acids provided an early example of organic photochemistry.

Occurrence and reactions

These compounds are found in a variety of plants, for example in coca. Incarvillateine, an alkaloid from the plant Incarvillea sinensis, is a derivative of α-truxillic acid.
Upon heating, truxillic acids undergo cracking to give cinnamic acid.

Isomers

Truxillic acid can exist in five stereoisomers.
Isomerabcdef
α-truxillic acid
COOHHHC6H5HCOOH
γ-truxillic acidCOOHHHC6H5COOHH
ε-truxillic acidHCOOHC6H5HHCOOH
peri-truxillic acidCOOHHC6H5HCOOHH
epi-truxillic acidCOOHHC6H5HHCOOH

Below are the five stereoisomers of truxillic acid, called alpha, gamma, epsilon, peri, and epi. These are shown both in a 2D skeletal diagram with stereocenters indicated and a 3D rendering of the structural geometry of the isomers themselves.