Chem-805 Identification of organic and inorganic compounds by spectroscopy

1. Chem-805Identification of organic and inorganic compounds by spectroscopy Mass Spectrometry fragmentation NMR Infrared Index MS

2. Fragmentation process There are 3 type of fragmentations: • Cleavage of s bond + . ---- C + ---- C – C ---- + . C ---- At heteroatom + . ---- C + ---- C – Z ---- + . Z ---- a to heteroatom + . C=Z + ---- C - C – Z ---- + ---- C . + . Z + . ---- C - C – Z ---- + ---- C = C

3. + . + . + Fragmentation process There are 3 type of fragmentations: • Cleavage of 2s bond (rearrangements) +. ---- C=C + ---- HC – C – Z ---- + HZ Retro Diels-alder McLafferty +. +.

4. Fragmentation process There are 3 type of fragmentations: • Cleavage of Complex rearrangements

5. Fragmentation rules in MS • Intensity of M.+ is Larger for linear chain than for branched compound • Intensity of M.+decrease with IncreasingM.W. (fatty acid is an exception) • Cleavage is favored at branching reflecting the Increased stability of the ionStability order: CH3+ < R-CH2+ < R R CH+ < C+ R R R R’ R CH R” Loss of Largest Subst. Is most favored

6. Illustration of first 3 rules (large MW)

7. Branched alkanes MW=170 M.+ is absent with heavy branching Fragmentation occur at branching: largest fragment loss

8. Illustration of first 3 rules (Linear alkane with Smaller MW) Molecular ion is stronger than in previous sample

9. Illustration of first 3 rules (Branched alkane with Smaller MW) 43 Molecular ion smaller than linear alkane Cleavage at branching is favored

10. Alkanes Rule 3 Cleavage Favored at branching Loss of Largest substituent Favored Rule1: intensity of M.+ is smaller with branching

11. Fragmentation rules in MS • Aromatic Rings, Double bond, Cyclic structures stabilizeM.+ • Double bond favor Allylic Cleavage Resonance – Stabilized Cation

12. Aromatic ring has stableM.+

13. Cycloalkane ring has stableM.+

14. + . + . + Fragmentation rules in MS • a) Saturated Rings lose a Alkyl Chain (case of branching) • Unsaturated Rings  Retro-Diels-Alder +. + -R.

15. +. +. Retro Diels-alder

16. Fragmentation rules in MS • Aromatic Compounds Cleave in b Resonance Stabilized Tropylium -R. Tropylium ion m/z 91

17. Tropylium ion

18. Fragmentation rules in MS • C-CNext to Heteroatom cleave leaving the charge on the Heteroatom - [RCH2] - [R2] larger

19. Fragmentation rules in MS • Cleavage of small neutral molecules(CO2, CO, olefins, H2O ….)Result often from rearrangement McLafferty - CH2=CH2 Ion Stabilized by resonance Y  H, R, OH, NR2

20. + CH2 CH CH Et CH2 CH +CH2 CH + CH CH Et Me Et Et Me Me 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/z = 83 M+ = 112

21. Alkenes

22. Aromatic compound

23. Alcohols

24. Hydroxy compounds - R3 If R1=H m/z 45, 59, 73 … Loss of largest group If R1=alkyl m/z 59, 73, 87 … – (H2O) M – (H2O) - H2O - CHR=CHR M – (H2O) – (C1=C2) Alkene

25. Phenol

27. Aromatic Ether Molecular ion is prominent -CO - R 1) C5H5 m/z 65 m/z 93 Cleavage in b of aromatic ring - CH2=CH2 2) Rearrangement m/z 94

28. B Aliphatic Ether Cleavage of C-C next ot Oxygen Loss of biggest fragment • + CH3—CH2 —O—CH2 —CH2 —CH2 —CH3 CH3—CH2 —O+ =CH2 m/z 59 CH3—CH2 —O—CH2+

29. Ether Rearrangement m/z 45 B H— CH3 CH3—CH2—CH —O —CH2 —CH3 CH =O+ —CH2 CH3 CH3 CH =O+H CH3 m/z 73 1- Cleavage of C-C next to Oxygen Box rearr. M·+ m/z 73 2- Cleavage of C-O bond: charge on alkyl m/z 45 Index MS MS-fragmentation-2