1. Teaching the Chlorine Rule
Ray A. Gross, Jr.
Prince George’s Community College

2. The 19th Biennial Conference on Chemical Education
July 31, 2006

4. Home of the boilermakers.

5. The Chlorine Rule
A way to analyze the mass spectra of BrmCln compounds, where m and n are small numbers.
J. Chem. Educ. 2004, 81,

8. Brm and Cln Clusters

10. What we (need to) know
The end cluster peaks for Brm compounds are always ~1:1 in intensity.
The end cluster peaks for Cln compounds are ~3:1 for Cl1, ~9:1 for Cl2, and ~3n:1 for Cln.
The number of significant cluster peaks is one more then the number of halogens, m + n.

11. New Idea
Bromine makes the same 1:1 contribution to the end peaks of a BrmCln spectrum that it makes to a Brm spectrum.

12. Which means
Differences in end-peak intensities are attributable to the number of Cl atoms only.

15. The Chlorine Rule
For BrmCln compounds, the intensity ratio of the leftmost to rightmost cluster peak rises with the nth power of three.
I = 3n

19. Structure begets properties!

21. Conclusions
The chlorine rule provides an efficient method for determining small numbers of Br and Cl atoms in an unknown’s mass spectrum.
It complements the nitrogen rule.

22. Acknowledgement
SDBS Website (accessed July 2006)