Cyclopropane intermediates in the rearrangement and fragmentation of olefinic molecular ions

Abstract

Methyl loss from deuterium-labelled molecular ions of 4-methyl-2-pentene, 2-methyl-2-pentene and 1,1,2-trimethylcyclopropane has been investigated for metastable molecular ions and for molecular ions formed by charge exchange with COS", XE" and CO". For metastable ion fragmentation reactions all three compounds exhibit very similar behavior and show specific and essentially equal loss of each of the original methyl groups as well as specific loss of a methyl where the hydrogens derive exclusively from the non-methyl hydrogens of the original molecules. The former results are interpreted in terms of interconversion of the three molecular ions through a ring-opened form of the trimethylcyclopropane molecular ion. The loss of the non-methyl hydrogens as CH, is interpreted in terms of isomerization to the 2,3-dimethyl-2-butene structure. With increasing internal energy direct allylic cleavage of the unrearranged methylpentene molecular ions increases in importance while the trimethylcyclopropane molecular ion shows an increased preference for loss of the C(2) methyl group. With increasing internal energy loss of the original non-methyl hydrogens as CH, decreases markedly in importance.

Intermediacy of ion neutral complexes in the fragmentation of short-chain dialkyl sulfides

“…Rearrangement reactions should, therefore, prevail over direct bond cleavages. For 2 the main processes are 10 As expected,˛-cleavage (m/z 75) is of minor importance. Loss of the S-C 2 H 5 group as compared with elimination from the butyl chain is much more favored than in the source reactions (2e , Tables 3 and 8, 17 : 21 and 63 : 39, respectively).…”