McLaffertey rearrangement.

nitrogen rule
malaffertey rearrangement
mass spectroscopy
mass fragmentation

1. 1 PRESENTED BY Mr. Darshan N U B Pharm ( M Pharm) M Pharmacy II Semester Dept. of Pharmaceutical Chemistry SACCP PRESENTING TO Dr. T. Yunus Pasha Professor and Head Dept. of Pharmaceutical Chemistry SACCP 1 Nitrogen rule and McLafferty rearrangement  

2.   McLafferty rearrangement   2

3.   Nitrogen rule The  nitrogen rule  states that a molecule that has no or even number of  nitrogen  atoms has an even nominal mass, whereas a molecule that has an odd number of  nitrogen  atoms has an odd nominal mass . 3

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6. Molecule : Ammonia Hydrazine TNT Caffeine Formula : N H 3 N 2 H 4 C 7 H 5 N 3 O 6 C 8 H 10 N 4 O 2 m/z  ( M ) : 17    32    227    194 One  nitrogen m/z  ( M ) is  odd Two  nitrogens m/z  ( M ) is  even Three   nitrogens m/z  ( M ) is  odd Four   nitrogens m/z  ( M ) is  even t.                                                                                                                                 6

7. The  McLafferty rearrangement  is a reaction observed in  mass spectrometry  during the fragmentation or dissociation of organic molecules. It is sometimes found that a molecule containing a keto -group undergoes β-cleavage, with the gain of the γ-hydrogen atom. When  hydrogen  is available at the gamma position on carbonyl compounds, these compounds go through a specific rearrangement due to the cleavage of multiple bonds, including the bonds at alpha and gamma positions. This reaction is known as the McLafferty rearrangement. 7

8. The McLafferty rearrangement is a characteristic fragmentation of the  molecular ion  of a carbonyl compound containing at least one gamma hydrogen ., e.g., 8

9. Hexan-2-one 9

10. The fragmentation of the molecule ions of hexan-2-one by  α-cleavage  at the  carbonyl group  . The α-cleavage at a carbonyl group gives rise to the stable  acetyl   cation CH 3 CO + ,  m / z  43, and to the  • C 3 H 7  radical, while transfer of an H atom from the γ-CH 2  group to the CO group accompanied by  cleavage  of the C(α)C(β) bond produces the  radical cation  of the  acetone   enol  and a  propene  molecule.   10

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13. The rearrangement involves a six-membered ring transition state in which the carbonyl group pulls off the gamma proton, splitting the molecule into two pieces. These pieces consist of an enol radical cation and a neutral alkene fragment. The enol radical cation is observed in the mass spectrum, while the neutral alkene fragment is not observed. 13

14. Any carbonyl compound that has hydrogen in the gamma position is likely to have a peak in the mass spectrum corresponding to the enol radical cation formed by the McLafferty rearrangement. Both ketones and aldehydes give prominent molecular ion peaks though the [M+] peak is more prominent in ketones. 14

15. Only ketones and aldehydes that do not undergo this rearrangement are those which lack a side chain that can donate a hydrogen atom to the pi system . 15