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

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

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  1. 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

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

  3. Isotopes of Br and Cl

  4. Mass Spectrometer

  5. Schematic diagram of a mass spectrometer

  6. Why Br and Cl? Molecular-ion peaks of C10H20Br1Cl1, C10H19Br2Cl1 and C10H18Br3Cl1.

  7. 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).

  8. Herbert C. BrownNobel Laureate Hydroboration-oxidation with BH3 (CHM 201) Reduction with NaBH4 (CHM 202/204)

  9. Lillian BergNVCC-Annandale

  10. Chlorine Constant

  11. Bromine Constant IM = 3n

  12. Theoretical Considerations Ideal Compounds Br (a:b) = 1:1 Cl (a:b) = 3:1 13C and 2H negligible

  13. 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

  14. 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

  15. Ideal Model = Binomial Pair (1a + 1b)m(3a + 1b)n Br1Cl1 3a2 + 4ab + 1b2 = 3:4:1

  16. 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)

  17. Roald Hoffmann-Nobel Laureate Conservation of orbital symmetry “Oxygen” Priestley vs Sheele Hoffmann Woodward Djerassi

  18. Gross giving lecture with Hoffmann, Djerassi and Woodward looking on.

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

  20. Results N = 2m4n N = 2m2n2n N = 2A2n Chem. Educ. 2003, 8, 182-186

  21. 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

  22. Follow-on to the Chlorine Rule • An automated A + 2 isotope-pattern analyzer (IPA) • IPA is on my website J. Chem. Educ., in press

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

  24. Molecular-Ion Data is Entered into the IPA The Excel program returns the A + 2 (Cl, Br, S) composition of the molecular formula

  25. 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.

  26. Acknowledgement: Mass Spectra from the Spectral Data Base System (SDBS)

  27. Ende

  28. Lecture attended by hordes of students eager to learn.

  29. Gross and Friends

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