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The Chemical Educator

ISSN: 1430-4171 (electronic version)

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Abstract Volume 8 Issue 3 (2003) pp 182-186

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

Ray A. Gross, Jr.

Department of Physical Sciences, Prince George’s Community College, Largo, MD 20774,
Received January 13, 2003. Accepted March 30, 2003

Published online: 18 April 2003

Abstract. 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.

Key Words:  In the Classroom; instrumental analysis; mass spectrometry; isotopes; chlorine; bromine

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Issue date: June 1, 2003

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