MASS-SPECTROMETRIC LOCATION OF TRIPLE BONDS IN FATTY-ACIDS AND FRAGMENTATION MECHANISMS OF N-ACYLPYRROLIDINES

Mass spectra of the pyrrolidide derivatives of isomeric octadecynoic acids are characterized by simple fragmentation patterns. Examination of the spectra indicates that if the triple bond in acetylenic fatty acids occurs between Δ5 and ω2, the unsaturation may be located by observing the most intense peak in each 14-amu cluster of fragments. An interval of 10 amu (rather than the usual 14) between fragments corresponding to Cn-2 and Cn-1 of the acyl moiety indicates a triple bond at Cn. Confirmation of triple bond location is provided by intense peaks at Cn-2 and Cn+2. The rule has been found valid for all isomers within this series including Δ15, which produces a spectrum similar to but distinguishable from Δ17. Derivatization is accomplished by heating the fatty acyl moiety (methyl ester, triglyceride, phospholipid, etc.) with pyrrolidine. Because derivatization is performed on the carboxyl group, quantitation is assured regardless of the number and type of substituent groups present in the molecule. Electron impact of Al-acylpyrrolidines produces fragments which arise from both amide-directed fragmentation (ADF) and substituent-directed fragmentation (SDF). ADF predominates in the acetylenic isomers which conform to the general rule for location of triple bonds. Simple spectra are obtained in which the position of the substituent group may be deduced directly without necessitating a library search. © 1979, American Chemical Society. All rights reserved.