CHM120H5 Lecture Notes - Natural Abundance, Bromine, Chemical Formula
Document Summary
When bromine is present in a compound, the m + 2 ion becomes very significant. This is because bromine is comprised of two isotopes (79br and 81br) in a nearly 1:1 ratio in naturally occurring substances. If a compound contains bromine, the m+ and m + 2 ions are present at almost equal intensities. As a result, the relative intensities of the molecular ion peak and its associated isotope peaks directly indicate the number of bromine atoms in the molecular formula. The peaks would be observed at 79br (79m/z), 81br (81m/z), 79br-79br (158m/z), 79br- The relative heights of the peaks would be the following: Highest peak when br2 is composed of 79br-79br and the lowest peak would be when it consists of 81br due to the percent abundance. The reason for this being that fragmentation of br2 to a bromine cation then gives rise to equal sized ion peak at 81br.
