Determination of the specific positions ofcis andtrans double bonds in polyenes.

A method is described for the determination of the positions and geometric configurations of double bonds in polyunsaturated fatty acids. The procedure consists of three steps: 1) Partial reduction of the double bonds with hydrazine under conditions which give high yields of monoenes. 2) Isolation of thecis- and thetrans-monoene fractions by thin-layer chromatography (TLC) directly or in the form of their ozonide derivatives. In the former technique, selective argentation is employed, in the latter, silicic acid adsorption. 3) Determination of the structure of the monoenes via reductive ozonolysis. The position of the double bonds is determined from the structures of the monoenes. Since thecis-monoenes are separated from thetrans-monoenes the geometric configuration of each double bond is determined.The method also provides a direct determination of the spacings of the internal double bonds and it may be employed for the determination of the structures of mixtures of fatty acids in conjunction with direct ozonolysis procedures. The various ramifications of the method are demonstrated on pure fatty acids and model mixtures thereof.