Two Equations for Analyzing the Mass Spectra of Compounds for Chlorine and Bromine Atoms

Compounds in which m bromine and n chlorine atoms have replaced hydrogen atoms in a pure hydrocarbon are analyzed. The variable N represents the smallest number of molecules that replicates a bulk sample of Br and Cl containing molecules. For dibromochloromethane N is 16, m is 2, n is 1, and the variable A equals the sum of m and n or 3. Two equations are derived for N in terms of n and A. The variables A and N may be found from a normalized isotope pattern—the pattern that results when the relative abundances of the molecular ions two amu apart in a mass spectrum are divided by the relative abundance of the highest-mass molecular ion. Problems in which the value of n is calculated from a theoretical isotope pattern by one derived equation and from relative abundance data by the other equation are exemplified. The equations for N might be useful as models for isotope studies or in courses involving molecular spectroscopy or mass spectrometry.