SummaryThe cis, trans, and positional configuration of alpha‐and beta‐eleostearic acids have been investigated. The maleic anhydride adducts of alpha‐and beta‐eleostearic acids were prepared and subjected to hydrogenation, selective epoxidation, and esterification. Two epoxy derivatives of the maleinated beta‐eleostearic acid were isolated and characterized. Infrared spectra of these maleic anhydride adducts and their various derivatives have been measured in the rock salt region, 2–12 microns. These infrared data together with chemical evidence have been used to confirm the structure of alpha‐eleostearic acid as 9‐cis, 11‐trans, 13‐trans octadecatrienoic acid and beta‐eleostearic acid as 9‐trans, 11‐trans, 13‐trans octadecatrienoic acid.Complete infrared spectra are presented for authentic samples of alpha‐and beta‐tung oil, China wood oil, oiticica oil, and alpha‐and beta‐eleostearic acids. Infrared absorption curves are presented, including the maleic anhydride adducts of alpha‐and beta‐eleostearic acids, various derivatives of these adducts and the following reference compouds: maleic anhydride, dimethyl maleate, dimethyl fumarate, the butadiene‐maleic anhydride adduct and its dimethyl ester.