A novel approach to double bond location in long-chain olefinic acids has been elaborated by means of "remote functional group modification". This method consists of converting the carboxylic acid into the corresponding 2-alkenyl-substituted heterocycle followed by measuring its 70 eV mass spectrum. The inherited tendency of random migration of the double bond along the aliphatic chain under electron impact is strongly suppressed by incorporating the terminal carboxyl group into a heterocycle. The derivatives thus prepared show more informative spectra which clearly indicate the site of unsatn. of the parent acids. Submilligram scale derivatization of the olefinic acids, as exemplified by the model compound oleic acid, and a comparison of the spectra of the resulting heterocycles as well as benzoxazole derivatives of selected carboxylic acids are described.

Key words: CHEMICAL MODIFICATION, MASS SPECTROGRAPHY, CYCLIZATION, UNSATURATED FATTY ACID, CHEMICAL BONDS, LOCALIZATION, HETEROCYCLIC COMPOUNDS, LONG CHAIN COMPOUND, OLEIC ACID P