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### The Chlorine Rule: An Analysis of Isotope Patterns of Compounds Containing Multiple Bromine and Chlorine Atoms

Ray A. Gross, Jr.

With an Introduction to the Isotope-Pattern Analyzer

My Reasons for this Presentation

- Present results obtained at PGCC
- Show that content found in textbooks can be improved
- Motivate students

Molecular-ion peaks of C10H20Br1Cl1, C10H19Br2Cl1 and C10H18Br3Cl1.

Premise

In lieu of pattern matching,it should be possible to determine the number of Br and Cl atoms in a molecular formula of a compound by analyzing the molecular-ion cluster (i.e., by cluster analysis).

Herbert C. BrownNobel Laureate

Hydroboration-oxidation

with BH3 (CHM 201)

Reduction with NaBH4

(CHM 202/204)

Lillian BergNVCC-Annandale

Bromine Constant

IM = 3n

Bromine Binomial

- Ratio (a:b) = 1:1
- (1a + 1b)m for Brm
- (1a + 1b)1 = 1a + 1b = 1:1
- (1a + 1b)2 = 1a2 + 2ab+ 1b2 = 1:2:1

Chlorine Binomial

- Ratio (a:b) = 3:1
- (3a + 1b)n for Cln
- (3a + 1b)1 = 3a + 1b = 3:1
- (3a + b)2 = 9a2 + 6ab + 1b2 = 9:6:1

(1a + 1b)m(3a + 1b)n = 1m3na(m+ n) + …. + 1m1nb(m+ n)

I(L/R) = 1m3n/1m1n

IM = 3n

Chlorine Rule:When I equals 1, 3, 9, 27 or 81; n is 0, 1, 2, 3, or 4, respectively, where n = number of chlorine atoms.

The number of bromine atoms m equals A – n.

J.Chem.Educ. 2004, 81, 1161-1168 (article available at front desk)

Roald Hoffmann-Nobel Laureate

Conservation of orbital symmetry

“Oxygen” Priestley vs Sheele

Hoffmann

Woodward

Djerassi

Gross giving lecture with Hoffmann, Djerassi and

Woodward looking on.

Structure Begets Properties

- Let’s examine structures.
- Assume 3:1 and 1:1 isotopic abundances of chlorine and bromine.
- Consider Brm, Cln and BrmClncompounds.

Summary Part I for BrmClnCompounds

- Derived a chlorine-rule equation, IM = 3n
- Applied it to find gross structures of unknowns
- Derived a unit-sample equation, N = 2A2n

Follow-on to the Chlorine Rule

- An automated A + 2 isotope-pattern analyzer (IPA)
- IPA is on my website

J. Chem. Educ., in press

Example of a Print Out of a Mass Spectrum in the Molecular-Ion Region

Molecular-Ion Data is Entered into the IPA Molecular-Ion Region

The Excel program returns the A + 2 (Cl, Br, S) composition of the molecular formula

Homework Assignment Molecular-Ion RegionforSelected Students

- Pick up slip from front desk
- Enter data from your slip into IPA
- Obtain the Cl, Br, S composition (e.g., Br1Cl2) and record it on your slip
- Write your name on the slip and turn it in next Tuesday.

Ende System (SDBS)

Lecture attended by hordes of students eager to learn. System (SDBS)

Gross and Friends System (SDBS)

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