The Chlorine Rule An Analysis of Isotope Patterns

The Chlorine Rule: An Analysis of Isotope Patterns of Compounds Containing Multiple Bromine and Chlorine Atoms With an Introduction to the Isotope-Pattern Analyzer Ray A. Gross, Jr. 1

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

Isotopes of Br and Cl a Low mass b High mass Ratio (a/b) Rounde Variable d # atoms ratio Br 79 (50. 69) 81 (49. 31) 1. 028 1: 1 m Cl 35 (75. 78) 37 (24. 22) 3. 129 3: 1 n 3

Mass Spectrometer 4

Schematic diagram of a mass spectrometer 5

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Why Br and Cl? Molecular-ion peaks of C 10 H 20 Br 1 Cl 1, C 10 H 19 Br 2 Cl 1 and C 10 H 18 Br 3 Cl 1. 8

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 molecularion cluster (i. e. , by cluster analysis). 9

Herbert C. Brown Nobel Laureate Hydroboration-oxidation with BH 3 (CHM 201) Reduction with Na. BH 4 (CHM 202/204) 10

Lillian Berg NVCC-Annandale 11

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Chlorine Constant 20

Bromine Constant IM = 3 n 21

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Theoretical Considerations Ideal Compounds Br (a: b) = 1: 1 Cl (a: b) = 3: 1 13 C and 2 H negligible 24

Bromine Binomial • Ratio (a: b) = 1: 1 • (1 a + 1 b)m for Brm • (1 a + 1 b)1 = 1 a + 1 b = 1: 1 • (1 a + 1 b)2 = 1 a 2 + 2 ab + 1 b 2 = 1: 2: 1 25

Chlorine Binomial • Ratio (a: b) = 3: 1 • (3 a + 1 b)n for Cln • (3 a + 1 b)1 = 3 a + 1 b = 3: 1 • (3 a + b)2 = 9 a 2 + 6 ab + 1 b 2 = 9: 6: 1 26

Ideal Model = Binomial Pair (1 a + m(3 a 1 b) + n 1 b) Br 1 Cl 1 2 3 a + 4 ab + 2 1 b = 3: 4: 1 27

Results (1 a + 1 b)m(3 a + 1 b)n = 1 m 3 na(m + n) + …. + 1 m 1 nb(m + n) I(L/R) = 1 m 3 n/1 m 1 n IM = 3 n 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) 28

Roald Hoffmann-Nobel Laureate Conservation of orbital symmetry “Oxygen” Priestley vs Sheele Hoffmann Djerassi Woodward 29

Gross giving lecture with Hoffmann, Djerassi and Woodward looking on. 30

Structure Begets Properties • Let’s examine structures. • Assume 3: 1 and 1: 1 isotopic abundances of chlorine and bromine. • Consider Brm, Cln and Brm. Cln compounds. 31

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Results N = 2 m 4 n N = 2 m 2 n N = 2 A 2 n Chem. Educ. 2003, 8, 182 -186 35

Summary Part I for Brm. Cln Compounds • Derived a chlorine-rule equation, IM = 3 n • Applied it to find gross structures of unknowns • Derived a unit-sample equation, N = 2 A 2 n 36

Follow-on to the Chlorine Rule • An automated A + 2 isotope-pattern analyzer (IPA) • IPA is on my website J. Chem. Educ. , in press 37

Example of a Print Out of a Mass Spectrum in the Molecular-Ion Region Mass 224 225 226 227 228 229 230 Percent 64. 4 4. 3 100. 0 6. 9 45. 6 3. 2 6. 4 38

Molecular-Ion Data is Entered into the IPA The Excel program returns the A + 2 (Cl, Br, S) composition of the molecular formula 39

Homework Assignment for Selected Students • Pick up slip from front desk • Enter data from your slip into IPA • Obtain the Cl, Br, S composition (e. g. , Br 1 Cl 2) and record it on your slip • Write your name on the slip and turn it in next Tuesday. 40

Acknowledgement: Mass Spectra from the Spectral Data Base System (SDBS) 41

Ende 42

Lecture attended by hordes of students eager to learn. 43

Gross and Friends 44