Fragmentation processes of methylbutyl trifluoroacetates studied by tandem quadrupole mass spectrometry and isotope labeling

Abstract

AbstractThe fragmentation patterns of 3‐methyl‐2‐butyl trifluoroacetate and 2‐methyl‐2‐butyl trifluoroacetate were investigated by GC/MS/MS, with electron impact and collision‐induced dissociation, on regular and isotope‐labeled (deuterium and 18O) esters. The atoms found in various fragments could be traced back to specific positions in the parent molecules. In this way, molecular rearrangements potentially occurring during the formation of esters by trifluoroacetolysis of 3‐methyl‐2‐butyl p‐toluenesulfonate or trifluoroacetic acid addition to various 2‐methylbutenes could be shown. Rearrangements also occurred during the fragmentation, particularly during the expulsion of the small fragments CO, C2H4 and F2CO. For the decompositions of oxygen‐containing ions these rearrangements were highly specific. By contrast, alkyl cations lead to fragments that are fully scrambled (statistical label distribution). Alkene radical cations ([CnH2n]+ ˙) fragment to daughter ions that are extensively, but less than statistically scrambled. Hydrogen scrambling may also occur in fluoroalkyl cation fragments.