Mass spectra of benzofurans

Abstract

The mass spectra of a number of substituted benzofurans are reported. Ring fragmentation as opposed to substituent fragmentation was observed in halogenated benzofurans. Initial loss of carbon monoxide was found without any evidence for loss of formyl radical (HCO). Benzocyclopropenecarboxaldehyde is proposed as a possible intermediate ion. Hydrogen scrambling observed with deuterated substrates occurred in either the molecular ion, the carboxaldehyde radical ion or the CO elimination product, the benzocyclopropene radical ion. The chlorobenzofurans and, in part, bromobenzofuran fragmented by successive loss of CO and halogen atom. The bromobenzfuran molecular ion also showed the inverted sequence of initial loss of bromine followed by loss of CO. This process was examined by use of the spectra of nitro- and methoxy-benzofurans. Fluorobenzofurans showed little fluorine loss in the early stages of the fragmentation process.