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MiniQuiz 8 Problem:

OH. O. N. NO. NH. 2. 2. 2. +. NO. 2. MiniQuiz 8 Problem:. Complete this reaction equation:. Today:. Mass Spectrometry Next time: H-NMR, CMR Following Tuesday (May 12): Your questions Final Exam in Lab. Mass Spectrometry Interpretation of Mass Spectra.

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MiniQuiz 8 Problem:

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  1. OH O N NO NH 2 2 2 + NO 2 MiniQuiz 8 Problem: Complete this reaction equation:

  2. Today: Mass Spectrometry Next time: H-NMR, CMR Following Tuesday (May 12): Your questions Final Exam in Lab

  3. Mass SpectrometryInterpretation of Mass Spectra Study Mass Spectrometry Chapters in Lab and Lecture Texts • Molecules of a sample are bombarded by a stream of high energy electrons • Molecular ion peak M+. • Molecular ion bonds break to give fragment IONS and NEUTRAL radicals or molecules. Mass Spectra only show ions, not neutrals. • m/z of M+ - m/z of F+ (fragment ion) = mass of neutral • Each peak can be interpreted in terms of both a fragment ion and/or a neutral loss

  4. Mass Spectrometry • Molecular ion peak (M+.) at m/z 32 • Base peak at m/z 31 • Fragment ions at 29 and 15 A Mass Spectrum tells you the molecular mass

  5. Molecular Ion Peak: Odd or Even Mass? aniline

  6. Isotope Peaks:35Cl and 37Cl

  7. Isotope Peaks:79Br and 81Br

  8. Molecular Ion Peak: Alcohols … 1-butanol MW: 74

  9. Favored Fragmentations • The greater the stability of the fragment ion, the more intense the peak • Alkyl ion stability follows carbocation chemistry rules: 3° and allyl more stable than 2° 2° more stable than 1° • Acyl ions are stable (m/z 43, 57..) • PhC=O+ (m/z 105…) • Alpha (a) cleavage in alcohols, amines, ethers • Aromatic rings do NOT fragment easily

  10. Characteristic Fragment Ions • Look for alkyl ions at m/z 43, 57, 71, 85 (14 amu or CH2 series)

  11. Fragmentation of alkanes

  12. Characteristic Fragment Ions • Look for aryl ions at 77 (phenyl), 91 (benzyl), and 105 (benzoyl)

  13. Fragmentation in Aromatics Tropylium Ion

  14. Characteristic Fragment Ions • Acyl ions are stable (m/z 43, 57..)

  15. Acyl Fragment acetophenone

  16. Characteristic Neutral Losses • 1 is H (e.g. from aldehydes) • 15 can only be methyl • 17 usually OH • 18 always H2O • 28 CO or CH2=CH2 • 29 CH3CH2 or CHO • 31 CH3O • 35/37 Cl (special isotope pattern too!) • 42 CH2=C=O • 43 CH3CO or C3H7 • 45 CH3CH2O or COOH • 79/81 Br (special isotope pattern too!)

  17. Weights of common fragments or neutral losses

  18. Mass SpectrometrySummary • Molecular weight: • odd-numbered (N ...) ? • isotope peaks (Cl, Br)? • Alcohols … • Recognize typical fragments: • H2O, alkyl, acyl, tropylium ion …

  19. Next time: • Bring Spectra of your Unknown #3! • Brief Review of Mass Spectroscopy • Discussion/Review of H-NMR, CMR

  20. OH O N NO NH 2 2 2 + NO 2 MiniQuiz Problem: Complete this reaction equation:

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