Vitamin E exists in nature in eight forms, each of which consists of a head section joined to either a saturated (phytyl) or an unsaturated (farnesyl) tail. The four compounds with the saturated tails are the tocopherols, and the four compounds with the unsaturated tails are the tocotrienols. There are four unique dihydrocoumarin head sections, distinguished by one of four substitution patterns and designated as α, β, γ, or δ. The alpha- forms are distinguished by their three substituted methyl groups and the delta- forms by their one substituted methyl group. The beta- and gamma- forms both have two substituted methyl groups, although at different structural positions (5,8-dimethyl and 7,8-dimethyl, respectively), making both beta / gamma tocotrienol as well as the beta / gamma tocopherol pairs of stereoisomer.
^Komiyama K, Iizuka K, Yamaoka M, Watanabe H, Tsuchiya N, Umezawa I (May 1989). "Studies on the biological activity of tocotrienols". Chemical & Pharmaceutical Bulletin (Tokyo)5 (37): 1369–71. PMID2630104.|accessdate= requires |url= (help)