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1
Mass Spectrometry - molecular ionization
MOLECULE
electron beam
e-
MOLECULE
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Mass Spectrometer
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MS to distinguish isomers
m/z = 84
+ CH3
m/z = 79
+ CH2CH3
m/z = 84 m/z = 56
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Mass Spectrometry Summary
Mass of the molecule
Molecular Formula
Fragments - Most stable carbocations (and radicals)
Can give idea about how the molecule was connected
Can often identify constitutional isomers
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Electromagnetic Spectrum
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Energy of a photon
E = h!
E = hc/!
= c! "x
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Molecular Vibrations
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IR Spectrometer
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Typical IR Spectra
= 1!
"10
Typical Ranges for common functional groups
4000 3500 3000 2500 2000 1500 1000 500
wavenumber, cm-1
O H
C H
C H
C H
C C
C N
C O
Strong
StrongBroad
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Octane IR Spectrum
C H 2850 - 2960 cm-1
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Octene IR Spectrum
C H 3020 - 3100 cm-1
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Heptyne IR Spectrum
C H 3300 cm-1 (strong) C 2100-2260 cm-1C
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Ethanol IR Spectrum
O H 3400-3650 cm-1 (strong, broad)
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Butyraldehyde IR Spectrum
O
H
O 1670-1780 cm-1 (strong)C
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Ethyl Acetate IR
O
O
O 1670-1780 cm-1 (strong)C
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Benzonitrile IR
CN
N 2100-2260 cm-1C
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Typical Ranges for common functional groups
4000 3500 3000 2500 2000 1500 1000 500
wavenumber, cm-1
O H
C H
C H
C H
C C
C N
C O
Strong
StrongBroad
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Functional Group Stretches
C H
C H
C H
O H
CC
NC
C O
Functional Group
Wavenumber
Range (cm-1)
Absorption Strength
2850-2960 medium-strong
3020-3100 medium
3300 strong
3400-3650 broad-strong
2100-2260 medium
1680-1750 strong
notes
below 3000
above 3000
above 3000
Infrared Stretching Absorptions