The document discusses the nitrogen rule and McLafferty rearrangement. The nitrogen rule states that molecules with an even number of nitrogen atoms have an even nominal mass, while molecules with an odd number of nitrogen atoms have an odd nominal mass. The McLafferty rearrangement is a reaction observed in mass spectrometry where a molecule containing a keto-group undergoes β-cleavage, transferring a hydrogen from the γ position to the carbonyl group. This reaction results in an enol radical cation and a neutral alkene fragment. Any carbonyl compound containing a hydrogen in the γ position is likely to undergo the McLafferty rearrangement during mass spectrometry.

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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
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Nitrogen rule and McLafferty rearrangement

2. McLafferty rearrangement
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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.
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6. Molecule: Ammonia Hydrazine TNT Caffeine
Formula: NH3 N2H4
C7H5N3O
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C8H10N4O2
m/z (M):
17
32 227 194
One nitrogen
m/z (M)
is odd
Two nitrogen
s
m/z (M)
is even
Three nitrog
ens
m/z (M)
is odd
Four nitroge
ns
m/z (M)
is even
•
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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.
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8. • The McLafferty rearrangement is a characteristic fragmentation of
the molecular ion of a carbonyl compound containing at least one
gamma hydrogen ., e.g.,
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9. Hexan-2-one
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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 CH3CO+, m/z 43, and to the •C3H7 radical,
• while transfer of an H atom from the γ-CH2 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.
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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.
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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.
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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 .
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