Ms 1

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mass spectra fragmentation

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Ms 1

  1. 1. Chem-805 Identification of organic and inorganic compounds by spectroscopy <ul><li>Mass Spectrometry </li></ul><ul><ul><li>fragmentation </li></ul></ul><ul><li>NMR </li></ul><ul><li>Infrared </li></ul>Index MS
  2. 2. Fragmentation process <ul><li>Cleavage of  bond </li></ul>There are 3 type of fragmentations: ---- C – C ---- ---- C + . C ---- + ---- C – Z ---- ---- C + . Z ---- + At heteroatom + . + .  to heteroatom ---- C - C – Z ---- C=Z + ---- C . + + . ---- C - C – Z ---- Z + . ---- C = C + + .
  3. 3. Fragmentation process <ul><li>Cleavage of 2  bond (rearrangements) </li></ul>There are 3 type of fragmentations: ---- HC – C – Z ---- ---- C=C + HZ + Retro Diels-alder + . + . McLafferty + . + + . + .
  4. 4. Fragmentation process <ul><li>Cleavage of Complex rearrangements </li></ul>There are 3 type of fragmentations:
  5. 5. Fragmentation rules in MS <ul><li>Intensity of M . + is Larger for linear chain than for branched compound </li></ul><ul><li>Intensity of M . + decrease with Increasing M.W. (fatty acid is an exception) </li></ul><ul><li>Cleavage is favored at branching  reflecting the Increased stability of the ion Stability order: CH 3 + < R-CH 2 + < </li></ul>R R CH + < C + R R R R R” CH R’ Loss of Largest Subst. Is most favored
  6. 6. Illustration of first 3 rules (large MW)
  7. 7. Branched alkanes MW=170 M . + is absent with heavy branching Fragmentation occur at branching: largest fragment loss
  8. 8. Illustration of first 3 rules (Linear alkane with Smaller MW) Molecular ion is stronger than in previous sample
  9. 9. Illustration of first 3 rules (Branched alkane with Smaller MW) Molecular ion smaller than linear alkane Cleavage at branching is favored 43
  10. 10. Rule 3 Alkanes Cleavage Favored at branching Loss of Largest substituent Favored Rule1: intensity of M . + is smaller with branching
  11. 11. Fragmentation rules in MS <ul><li>Aromatic Rings, Double bond, Cyclic structures stabilize M . + </li></ul><ul><li>Double bond favor Allylic Cleavage  Resonance – Stabilized Cation </li></ul>
  12. 12. Aromatic ring has stable M .+
  13. 13. Cycloalkane ring has stable M .+
  14. 14. Fragmentation rules in MS <ul><li>a) Saturated Rings lose  Alkyl Chain (case of branching) </li></ul><ul><ul><li>Unsaturated Rings  Retro-Diels-Alder </li></ul></ul>+ . + -R . + + . + .
  15. 15. Retro Diels-alder + . + .
  16. 16. Fragmentation rules in MS <ul><li>Aromatic Compounds Cleave in   Resonance Stabilized Tropylium </li></ul>-R . Tropylium ion m/z 91
  17. 17. Tropylium ion
  18. 18. <ul><li>C-C Next to Heteroatom cleave leaving the charge on the Heteroatom </li></ul>Fragmentation rules in MS - [RCH 2 ]  - [R 2 ]  larger
  19. 19. Fragmentation rules in MS <ul><li>Cleavage of small neutral molecules (CO 2 , CO, olefins, H 2 O ….) Result often from rearrangement </li></ul>McLafferty Y  H, R, OH, NR2 Ion Stabilized by resonance - CH 2 =CH 2
  20. 20. Alkenes Most intense peaks are often: m/z 41, 55, 69 Rule 4: Double Bond Stabilize M  + Rule 5: Double Bond favor Allylic cleavage -Et  -29 M  + = 112 m/z = 83 CH 2 CH CH  + Et Et Me + CH 2 CH CH Et Me CH 2 CH CH + Et Me
  21. 21. Alkenes
  22. 22. Aromatic compound
  23. 23. Alcohols
  24. 24. Hydroxy compounds Loss of largest group - R 3  If R 1 =H m/z 45, 59, 73 … If R 1 =alkyl m/z 59, 73, 87 … M – (H 2 O) – (C1=C2) Alkene - H 2 O - CHR=CHR M – (H 2 O) – (H 2 O)
  25. 25. Phenol
  26. 27. Aromatic Ether Molecular ion is prominent 1) Cleavage in  of aromatic ring Rearrangement 2) C 5 H 5 -CO m/z 93 m/z 65 - CH 2 =CH 2 m/z 94 - R 
  27. 28. Aliphatic Ether CH 3 —CH 2 —O—CH 2 —CH 2 —CH 2 —CH 3 CH 3 —CH 2 —O + =CH 2 CH 3 —CH 2 —O —CH 2 + • + Cleavage of C-C next ot Oxygen Loss of biggest fragment m/z 59 B
  28. 29. Ether Rearrangement Index MS MS-fragmentation-2 Box rearr. 1- Cleavage of C-C next to Oxygen m/z 73 m/z 45 M ·+ 2- Cleavage of C-O bond: charge on alkyl m/z 73 m/z 45 B CH 3 —CH 2 —CH —O —CH 2 —CH 3 CH 3 CH =O + —CH 2 CH 3 H — CH 3 CH =O + H CH 3

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