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Factoring Isotope Patterns A + 2 Elements (O, S and Si)

Ray A. Gross, Jr.Prince George’s Community College

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Outline

• Derive a chlorine-rule equation for BrmCln

compounds

• Expand the equation to include oxygen, sulfur and silicon

• Apply the factoring technique to isotope patterns of Br1S1, Cl1S1 and Br1Cl1S1 compounds

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Derivation

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

I = 1m3n/1m1n

I = 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 the number of peaks attributable to m and n minus the sum of n + 1.

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M = 224

Br

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224149 = Br1Cl2 75 = benzene residue

1.0

Figure 1. Mass spectrum of 1-bromo-2,4-dichlorobenzene.

Cl

Cl

The number of A+ 2 peaks = 4. I = 10/1.0 = 3n

n = 2 = Cl2

m = 4 - 3 = 1 = Br1

Compound contains Br1Cl2

62 100 45 6

10 : 17 : 8 : 1

9 Cl Cl BrUnknown10 : 17 : 8 : 1

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A + 2 Elements

Element A (%) A + 2 (%) Model factor

Variable

Bromine 79 (51) 81 (49) 1:1 m

Chlorine 35 (76) 37 (24) 3:1 n

Oxygen 16 (99.8) 18 (0.2) 500:1 p

Sulfur 32 (95) 34 (4) 22:1 q

Silicon 28 (92) 30 (3) 30:1 r

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General A + 2 Model

(a + b)m(3a + b)n(500a + b)p(22a + b)q(30a + b)r

The expression reverts to the binomial pair (a + b)m(3a + b)n when p, q and r equal zero.

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(a + b)1(500a + b)1

500a2 + 501ab +1b2

100 : 100 : 0.2

T = m + p + 1 = m + 1

Br1O1

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(3a + b)1(500a + b)1

1500a2 + 503ab +1b2

100 : 34 : 0.07

T = n + p + 1 = n + 1

Cl1O1

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147 190 46

3:4:1

Unknown

OHCl

Br

3:4:13 Cl Br

206114 = Br1Cl1 92 76 = Ph 16 = O

Figure 3. Mass spectrum of 4-bromo-2-chlorophenol.

M = 206

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(a + b)1(22a + b)1

22a2 + 23ab +1b2

22 : 23 : 1

T = m + q + 1

Br1S1

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Figure 5. Mass spectrum of o-bromothiophenol.

M = 188

100 46 47 2

23 : 24 : 1

23 : 24 : 122 S Br

188111 = Br1S1 77 = Ph + H

SHBr

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(3a + b)1(22a + b)1

66a2 + 25ab +1b2

66 : 25 : 1

T = n + q + 1

Cl1S1

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S

Cl

M = 118

190 71 3

63 : 24 : 1

Figure 6. Mass spectrum of 3-chlorothiophene.

63 : 24 : 1

66 S Cl

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(a + b)1(3a + b)1(22a + b)1

66a3 + 91a2b + 26ab + 1b2

66 : 91 : 26 : 1

T = m + n + q + 1

Br1Cl1S1

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Unknown139 187 52 2

M = 196

70 : 94 : 26 : 1

Figure 7. Mass spectrum of 2-bromo-5-chlorothiophene.

M + 6

70 : 94 : 26 : 1 66 S Cl Br

196146 = Br1Cl1S1 50 = C4H2

S BrCl

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I.P. I (T) Structure

1:1 1(2) Cl0

3:1 3(2) Cl1

9:6:1 9(3) Cl2

22:1 22(2) S1

27:27:9:1 27(4) Cl3

30:1 30(2) Si1

66:25:1 66(3) Cl1S1

81:108:54:12:1 81(5) Cl4

90:33:1 90 (3) Cl1Si1

Structure = Function of I and T

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General A + 2 Equation

IM = 3n22q30r

T = m + n + q + r + 1

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Model for Br1Si1

• IM = 3n22p30r = 30

• T = m + r + 1 = 3

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Analyze 27:27:1

30 Si Br27:27:127 Cl Cl Cl

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Summary

Gross structures of some aromatic compounds that contain C, H, Br, Cl, O and S can be determined by factoring their A + 2 mass spectral clusters.

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Acknowledgements• Junhua Yan’s Isotope Pattern Calculator

http://www.geocities.com/junhuayan/pattern.htm (accessed May 2003).

• Institute of Advanced Industrial Science and Technology; Tsukuba, Ibaraki, Japan

SDBSWeb: http://www.aist.go.jp/RIODB/SDBS/ (accessed May 2003).

• NIST Data Base, http://physics.nist.gov/PHYsRefData/Compositions/index.html

• (accessed Jul 2003).

• NSF Grant: DUE-0202431

• Chlorine Rule, in press JCE