The hydrocarbon chains on either side of the cisolefin group in 13-docosenoic acid adopt all-trans conformation and form an orthorhombic subcell with parallel skeletal planes. Both the methyl- and carboxyl-terminal polymethylene chains are inclined toward the interface of the dimer layers by 34 °. The torsion angles of the cis-olefin group, C--C--C--C--C--C , are -129, 0 and 127 ° from the carboxyl side.