Mass Spectrometry - CFQ & PP: Mass Spectrometry Reading...

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88 Reading Brown and Foote: Sections 14.1 and 14.2 Lecture Handout Mass Spectrometry (page 14 of this Thinkbook) Optional Web Site Reading A History of Mass Spectrometry ( The Organic Chemistry Virtual Tutor: Mass Spectrometry ( The Nobel Prize in Chemistry 1996: Discovery of C 60 ( Chemistry Catches Cocaine at Source ( Suggested Text Exercises Brown and Foote Chapter 14: 1, 5 – 12, 18, 19, 37 Optional Interactive Organic Chemistry CD and Workbook Spectroscopy: Mass Spectrometry (p. 63) The natural abundance of isotopes table included in the lecture handout does not need to be memorized. Working lots of problems will help you become familiar with the numbers. The data will be given on an exam if needed. Concept Focus Questions 1. Define the following terms. (a) Base peak (c) Fragmentation (e) M/z (b) DBE (d) Molecular Ion (f) Radical cation 2. How is the DBE count for a compound determined? What does this number mean? 3. Briefly describe how a mass spectrometer works. 4. Thompson and Aston observed that the mass spectrum of neon is as follows: m/z 20 (90% abundance) and m/z 22 (10%). What conclusions can be drawn from this data? 5. How is mass spectrometry used to determine in a person has been taking a drug of abuse such as cocaine? 6. How can it be determined if a peak in the mass spectrum is the molecular ion? 7. What is the significance of the M, M + 1 and M + 2 peaks in a mass spectrum? 8. What is the C n H 2n + 2 rule?
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CFQ & PP: Mass Spectrometry 89 9. What is the nitrogen rule? 10. Why does fragmentation occur? 11. What controls which bonds in a molecule are broken during fragmentation? Concept Focus Questions Solutions 1. (a) Base peak: The peak corresponding to the most abundant ion in the mass spectrum (the tallest peak). (b) DBE: Double Bond Equivalent. One DBE = one π bond or one ring. (c) Fragmentation: The process by which an ion breaks into smaller pieces. (d) Molecular ion: An ion of the molecule introduced into the mass spectrometer hat has lost one electron but has not yet fragmented. (e) M/z: Mass-to-charge ratio; the horizontal scale of a mass spectrum. (f) Radical cation: An ion that has both a positive charge and an unpaired electron. 2. DBE = Tet - (Mono/2) + (Tri/2) + 1, where: Tet = number of tetravalent atoms (usually only carbon) Mono = number of monovalent atoms (usually hydrogen or halogens), and Tri = number of trivalent atoms (usually only nitrogen). Each DBE corresponds to one π bond or one ring. Example: For the formula C
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Mass Spectrometry - CFQ & PP: Mass Spectrometry Reading...

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