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Teaching the Chlorine Rule

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Teaching the Chlorine Rule

Ray A. Gross, Jr.

Prince George’s Community College

The 19th Biennial Conference on Chemical Education

July 31, 2006

Home of the boilermakers.

A way to analyze the mass spectra of BrmClncompounds, where m and n are small numbers.

J. Chem. Educ.2004, 81, 1162-1168

- 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.

- Bromine makes the same 1:1 contribution to the end peaks of a BrmClnspectrum that it makes to a Brm spectrum.

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

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

Structure begets properties!

- 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.

- SDBS Website http://www.aist.go.jp/RIODB/SDBS/cgi-bin/cre_index.cgi (accessed July 2006)