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Mechanism of Phenylurethane

Mechanism of Phenylurethane. 1-butanol and phenyl isocyanate. Mass Spectrometry Interpretation of Mass Spectra. Check 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 +.

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Mechanism of Phenylurethane

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  1. Mechanism of Phenylurethane 1-butanol and phenyl isocyanate

  2. Mass SpectrometryInterpretation of Mass Spectra Check 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

  3. 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

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

  5. Isotope Peaks:35Cl and 37Cl

  6. Isotope Peaks:79Br and 81Br

  7. Molecular Ion Peak: Alcohols … 1-butanol

  8. 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

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

  10. Fragmentation of alkanes

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

  12. Fragmentation in Aromatics Tropylium Ion

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

  14. Acyl Fragment acetophenone

  15. Characteristic Neutral Losses • 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!)

  16. Weights of common fragments or neutral losses

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

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

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