Chemical modification in mass spectrometry.1.The double bond location of long-chain fatty acids:The mass spectra of 2-alkenyl substituted heterocycles

A novel approach to double bond location in long-chain olefinic acids has been elaboratedby means of“remote functional group modification”.This method consists in converting the car-boxylic acid into corresponding 2-alkenyl substituted heterocycle followed by measuring its 70 eVelectron-impact mass spectrum.The inherited tendency of random migration of the double bondalong the aliphatic chain under electron impact is strongly suppressed by incorporating the terminalcarboxyl group into a heterocycle.The derivatives thus prepared show more informative spectrawhich clearly indicate the site of unsaturation of the parent acids.Submilligram scale derivatizationof the olefinic acids,as exemplified by the model compound oleic acid,and a comparison of the spectraof the resulting heterocycles(3—10)as well as benzoxazole derivatives(3a—3d)of selected carboxylicacids is described in the present paper.