Fragmentation of Monosubstituted Cyclopentenes Under Electron Impact Mass Spectrometry

Abstract

Decomposition of 1- and 3-monosubstituted cyclopentene hydrocarbons with n-alkyl (C1-C8), isoalkyl (C3-C5), allyl, phenyl and benzyl substituents is influenced by the structure, length and position of the side chain. The stability of the molecular ion depends on the degree of substitution at the double bond, and is higher for 1-isomers than for 3-isomers. At low energies n-alkyl- cyclopentenes >C9 decompose mainly via cleavage of the β-C-C-bond to the ring with hydrogen atom rearrangement to form ions with m/e 82, small n-alkyl substituents C1-C3 eliminate directly from the molecular ion to form ions with m/e 67. At 50 eV the main fragmentation reaction is elimination of the substituent and formation of ions (C5H7)+. Degradation of 3-n-alkylcyclopentenes >C7 results in larger quantities (about 1.5 times) of ions (C5H7)+ in comparison with 1-isomers. On the basis of quantitative differences in the spctra, a scheme for the indentification of isomeric n-alkylcyclopentenes >C9 is given.