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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

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slide1

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
My Reasons for this Presentation
  • Present results obtained at PGCC
  • Show that content found in textbooks can be improved
  • Motivate students
slide8

Why Br and Cl?

Molecular-ion peaks of C10H20Br1Cl1, C10H19Br2Cl1 and C10H18Br3Cl1.

premise
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 brown nobel laureate
Herbert C. BrownNobel Laureate

Hydroboration-oxidation

with BH3 (CHM 201)

Reduction with NaBH4

(CHM 202/204)

theoretical considerations
Theoretical Considerations

Ideal Compounds

Br (a:b) = 1:1

Cl (a:b) = 3:1

13C and 2H negligible

bromine binomial
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
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
slide27

Ideal Model = Binomial Pair

(1a + 1b)m(3a + 1b)n

Br1Cl1

3a2 + 4ab + 1b2 = 3:4:1

slide28

Results

(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
Roald Hoffmann-Nobel Laureate

Conservation of orbital symmetry

“Oxygen” Priestley vs Sheele

Hoffmann

Woodward

Djerassi

structure begets properties
Structure Begets Properties
  • Let’s examine structures.
  • Assume 3:1 and 1:1 isotopic abundances of chlorine and bromine.
  • Consider Brm, Cln and BrmClncompounds.
results
Results

N = 2m4n

N = 2m2n2n

N = 2A2n

Chem. Educ. 2003, 8, 182-186

slide36

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
Follow-on to the Chlorine Rule
  • An automated A + 2 isotope-pattern analyzer (IPA)
  • IPA is on my website

J. Chem. Educ., in press

molecular ion data is entered into the ipa
Molecular-Ion Data is Entered into the IPA

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

homework assignment for selected students
Homework AssignmentforSelected 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.
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