Mass Spectra for Molecular Structure(5) Mass Spectra of Methyl Esters of 2-Alkenic Acid(part 2)

Abstract

Mass spectra of methyl esters of 2-alkenic acids, and those of terpenic compounds were measured by electron impact ionization.
The fragmentation patterns of a pair of isomers in methyl esters of nonbranched and branched 2-alkenic acids differ markedly. The fragment ion at m/e113 from nonbranched cis-esters appears more strongly than that from nonbranched transesters, and the fragment ion at m/e87 from nonbranched trans-esters is more abundant, than nonbranched cis-esters.
The corresponding fragment ion at m/e113 appears characteristically in the mass spectrum of branched cis-esters, but the fragment ion at m/e87 appears only in the mass spectrum of methyl 2-methyl-trans-2-octenate[22].
On the other hand, the similarity of the fragmentation patterns of a pair of isomers in the mass spectrum of methyl esters of terpenic acids was discussed on the basis of the spectrum of homologous compounds of methyl geranate. It is suggested that the cleavage of alkyl groups of the terpenic comounds of fects the fragmentation patterns.