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Mass Spectrometry

Mass Spectrometry. Only Cations are Detected. Ionization to Radical Cation Molecular Ion (m + ). Glossary. Molecular ion - The ion obtained by the loss of one electron from the molecule (m + ) Base peak - The most intense peak in the MS, assigned 100% intensity

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Mass Spectrometry

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  1. Mass Spectrometry

  2. Only Cations are Detected

  3. Ionization to Radical CationMolecular Ion (m+)

  4. Glossary • Molecular ion - The ion obtained by the loss of one electron from the molecule (m+) • Base peak-The most intense peak in the MS, assigned 100% intensity • Radical cation-positively charged species with an odd number of electrons • Fragment ions - Lighter cations (and radical cations) formed by the decomposition of the molecular ion.  These often correspond to stable carbcations. • m/z-mass to charge ratio

  5. Methanol

  6. Octane, m+ = 114 m-71 Base peak m-57 m-29 m-43 m+

  7. Isooctane, no molecular ion

  8. Decane

  9. 2-Methylpentane

  10. Effect of Branching in Hydrocarbons

  11. Isotopes • Mass spectrometers are capable of separating and detecting individual ions even those that only differ by a single atomic mass unit. • As a  result molecules containing different isotopes can be distinguished. • This is most apparent when atoms such as bromine or chlorine are present (79Br : 81Br, intensity 1:1 and 35Cl : 37Cl, intensity 3:1) where peaks at "M" and "M+2" are obtained. • The intensity ratios in the isotope patterns are due to the natural abundance of the isotopes. • "M+1" peaks are seen due the the presence of 13C in the sample.

  12. Bromomethane

  13. 1-Bromopropane

  14. 2-Chloropropane

  15. (3-Chloropropyl)benzene

  16. Chloroacetone

  17. 3-Pentanone m-29 base m+

  18. 2-Pentanone m-43 base m+ m-15

  19. (E) 2-Hexene

  20. 2-methyl-2-penteneand2-hexene

  21. 1-Butanol m-18

  22. 1o Alcohols: Loss of H2O

  23. Toluene m-1 m+

  24. Propylbenzene m-29 m+

  25. Isopropylbenzene m-15 m+

  26. n-Butylbenzene

  27. 3-Methyl-1-penten-3-ol m/z = 71 m+

  28. 4-Methyl-1-penten-3-ol m/z = 57 m+

  29. McLafferty Rearrangementlink to SDBS

  30. McLafferty Rearrangements in Alkyl Benzenes

  31. Benzamide

  32. 2-Octanone

  33. 2-Octanone

  34. Decanoic Acid

  35. p-Chloroacetophenone

  36. Methyl Octanoate

  37. 2,4-Dimethoxyacetophenone

  38. Cyclohexanone

  39. High Resolution Mass SpectrometryDetermination of Molecular Formula

  40. Isotope Ratios Can Help to Determine Molecular Formula Relative intensities (%) MFMWMM+1M+2 CO 28.0 100 1.12 0.2 N2 28.0 100 0.76 ---- C2H4 28.0 100 2.23 0.01

  41. Comparisons of Molecular Weights and Precise Masses MFMWexact mass C3H8O 60.1 60.05754 C2H8N2 60.1 60.06884 C2H4O2 60.1 60.02112 CH4N2O 60.1 60.03242

  42. Determine the Formulafragment finder

  43. Determine the Formula

  44. Subtract Sulfur’s contributionfragment finder

  45. Determine the Molecular Formula

  46. Compound gives four signals in the C-13 NMR spectrum

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