The mass spectrometry of some substituted imidazoles

Abstract

Mass spectra have been obtained for a number of substituted imidazoles using electron impact ionization and ammonia chemical ionization. Iodination of 1,2-[2H2]imidazole gave rise to diiododideuteroimidazole, suggesting iodination had taken place in the 4,5 positions and not 2,4 as previously thought. This compound was examined using both ammonia and [2H3]ammonia as reagent gases. Exchange of H-1 and partial exchange of iodine for proton was shown to occur in the chemical ionization source. A number of isomeric halomethyl-nitroimidazoles were also examined to explain observed differences in the spectra. The 4-nitroimidazoles apparently fragment to give an aziridinone ion, whereas the 5-nitro isomers appear to fragment to a cyclopropenone. Substitution of the halogen in the nitroimidazoles does not appear to occur so readily.