11 CHEM 344 Organic Chemistry Lab September 9 th and 10 th 2008 Spectroscopy of Organic Compounds...
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![Page 1: 11 CHEM 344 Organic Chemistry Lab September 9 th and 10 th 2008 Spectroscopy of Organic Compounds Lecture 3 –Infrared and Mass Spec.](https://reader036.fdocuments.us/reader036/viewer/2022081515/5697bfad1a28abf838c9c0d6/html5/thumbnails/1.jpg)
11
CHEM 344Organic Chemistry Lab
September 9th and 10th 2008
Spectroscopy of Organic Compounds
Lecture 3 –Infrared and Mass Spec
![Page 2: 11 CHEM 344 Organic Chemistry Lab September 9 th and 10 th 2008 Spectroscopy of Organic Compounds Lecture 3 –Infrared and Mass Spec.](https://reader036.fdocuments.us/reader036/viewer/2022081515/5697bfad1a28abf838c9c0d6/html5/thumbnails/2.jpg)
Infrared radiation excites vibrational energy levels of a molecule
Bond stretching, bending, twisting, rocking etc.
IR spectroscopy most useful for functional group assignment
IR bands reported in wavenumbers (cm-1)
![Page 3: 11 CHEM 344 Organic Chemistry Lab September 9 th and 10 th 2008 Spectroscopy of Organic Compounds Lecture 3 –Infrared and Mass Spec.](https://reader036.fdocuments.us/reader036/viewer/2022081515/5697bfad1a28abf838c9c0d6/html5/thumbnails/3.jpg)
4000 3000 2000 1600 400
Wavenumber (cm-1)
N – H
O – H
C – H (sp > sp2 > sp3)
C≡C
C≡N
C=C
C=N
C=O
Fingerprint region
Tra
nsm
itta
nce
(%)
100
0
Alkynes
Nitriles
Alkenes
Imines
Carbonyls
C-C
C-O
C-X
C-N
IR correlation tables in lab manual, textbook
Not used in CHEM 344
![Page 4: 11 CHEM 344 Organic Chemistry Lab September 9 th and 10 th 2008 Spectroscopy of Organic Compounds Lecture 3 –Infrared and Mass Spec.](https://reader036.fdocuments.us/reader036/viewer/2022081515/5697bfad1a28abf838c9c0d6/html5/thumbnails/4.jpg)
N-H
3281 cm-1
2900-3000 cm-1
sp3 C-H
2o amine R2NH
![Page 5: 11 CHEM 344 Organic Chemistry Lab September 9 th and 10 th 2008 Spectroscopy of Organic Compounds Lecture 3 –Infrared and Mass Spec.](https://reader036.fdocuments.us/reader036/viewer/2022081515/5697bfad1a28abf838c9c0d6/html5/thumbnails/5.jpg)
asym N-H
3369 cm-1
3291 cm-1
sym N-H
2900-3000 cm-1
sp3 C-H
1o amine RNH2
Sym and asym N-H bands typical of 1o amine RNH2
![Page 6: 11 CHEM 344 Organic Chemistry Lab September 9 th and 10 th 2008 Spectroscopy of Organic Compounds Lecture 3 –Infrared and Mass Spec.](https://reader036.fdocuments.us/reader036/viewer/2022081515/5697bfad1a28abf838c9c0d6/html5/thumbnails/6.jpg)
C≡C
2120 cm-1
sp3 C-H
sp C-H3315 cm-1
Terminal alkyne
![Page 7: 11 CHEM 344 Organic Chemistry Lab September 9 th and 10 th 2008 Spectroscopy of Organic Compounds Lecture 3 –Infrared and Mass Spec.](https://reader036.fdocuments.us/reader036/viewer/2022081515/5697bfad1a28abf838c9c0d6/html5/thumbnails/7.jpg)
2260 cm-1
Nitrile
C≡N
![Page 8: 11 CHEM 344 Organic Chemistry Lab September 9 th and 10 th 2008 Spectroscopy of Organic Compounds Lecture 3 –Infrared and Mass Spec.](https://reader036.fdocuments.us/reader036/viewer/2022081515/5697bfad1a28abf838c9c0d6/html5/thumbnails/8.jpg)
O-H3639 cm-1
C=O1698 cm-1
C-O band in fingerprint region
![Page 9: 11 CHEM 344 Organic Chemistry Lab September 9 th and 10 th 2008 Spectroscopy of Organic Compounds Lecture 3 –Infrared and Mass Spec.](https://reader036.fdocuments.us/reader036/viewer/2022081515/5697bfad1a28abf838c9c0d6/html5/thumbnails/9.jpg)
1685 cm-1
C=O
1619 cm-1
C=C
sp2 sp3 C-
H
C=O usually most intense band in IR spectrum
C=O and C-C in same region (1700 – 1600 cm-1) – which is which?
![Page 10: 11 CHEM 344 Organic Chemistry Lab September 9 th and 10 th 2008 Spectroscopy of Organic Compounds Lecture 3 –Infrared and Mass Spec.](https://reader036.fdocuments.us/reader036/viewer/2022081515/5697bfad1a28abf838c9c0d6/html5/thumbnails/10.jpg)
OC
Et
HO
1716 cm-1
OC
Et
HO
O C
Et
OH
2800 - 2600 cm-
1
Broad band typical of RCO2H
![Page 11: 11 CHEM 344 Organic Chemistry Lab September 9 th and 10 th 2008 Spectroscopy of Organic Compounds Lecture 3 –Infrared and Mass Spec.](https://reader036.fdocuments.us/reader036/viewer/2022081515/5697bfad1a28abf838c9c0d6/html5/thumbnails/11.jpg)
Mass Spectrometry
Uses high energy electron beam (70 eV), sample in gas phase
Ionization potential for most organic molecules 8-15 eV
Gives info on molecular weight of compound by m/z
Gives info on connectivity of molecule by fragmentation pattern
![Page 12: 11 CHEM 344 Organic Chemistry Lab September 9 th and 10 th 2008 Spectroscopy of Organic Compounds Lecture 3 –Infrared and Mass Spec.](https://reader036.fdocuments.us/reader036/viewer/2022081515/5697bfad1a28abf838c9c0d6/html5/thumbnails/12.jpg)
M + e [M] + 2 e
Molecular Fragments
Molecule
Molecular Ion
[M].+ (also called the parent peak) gives the mass of the molecule
Fragments give info on connectivity (i.e. structure) of the molecule
![Page 13: 11 CHEM 344 Organic Chemistry Lab September 9 th and 10 th 2008 Spectroscopy of Organic Compounds Lecture 3 –Infrared and Mass Spec.](https://reader036.fdocuments.us/reader036/viewer/2022081515/5697bfad1a28abf838c9c0d6/html5/thumbnails/13.jpg)
Mass Spectrum of methanol CH3OH
32
31
29
15
Base peak
[M]+.
m/z = mass/charge ratio
In CHEM 344, we only consider singly charged species (i.e. z=1)
The most intense peak is referred to as the base peak
All other peaks measured relative to base peak
![Page 14: 11 CHEM 344 Organic Chemistry Lab September 9 th and 10 th 2008 Spectroscopy of Organic Compounds Lecture 3 –Infrared and Mass Spec.](https://reader036.fdocuments.us/reader036/viewer/2022081515/5697bfad1a28abf838c9c0d6/html5/thumbnails/14.jpg)
[M]
Cation stability more important than radical stability
Molecular Ion
Cation radical
A + B
Cation
Radical
A + B
Cation
Radical
Radicals are not detected by MS
![Page 15: 11 CHEM 344 Organic Chemistry Lab September 9 th and 10 th 2008 Spectroscopy of Organic Compounds Lecture 3 –Infrared and Mass Spec.](https://reader036.fdocuments.us/reader036/viewer/2022081515/5697bfad1a28abf838c9c0d6/html5/thumbnails/15.jpg)
Mass Spectrum of methanol CH3OH
32
31
29
15
[CH2OH]+
Base peak
[CHO]+
[CH3]+
[CH3OH]+.
[M].+
![Page 16: 11 CHEM 344 Organic Chemistry Lab September 9 th and 10 th 2008 Spectroscopy of Organic Compounds Lecture 3 –Infrared and Mass Spec.](https://reader036.fdocuments.us/reader036/viewer/2022081515/5697bfad1a28abf838c9c0d6/html5/thumbnails/16.jpg)
Mass Spectrum of 2,2,4-trimethylpentane
57
43
Me Me
MeMe
Me
MW=114C8H18
Me
Me
Me
C
Me
Me H
3o carbocation
2o carbocation
No [M].+ detected
![Page 17: 11 CHEM 344 Organic Chemistry Lab September 9 th and 10 th 2008 Spectroscopy of Organic Compounds Lecture 3 –Infrared and Mass Spec.](https://reader036.fdocuments.us/reader036/viewer/2022081515/5697bfad1a28abf838c9c0d6/html5/thumbnails/17.jpg)
Mass Spectrum of 1-butanol
5631
43
29
CH2=OH
via loss of H2OCH3CH2
OH
C4H10O MW = 74
No [M].+ detected
![Page 18: 11 CHEM 344 Organic Chemistry Lab September 9 th and 10 th 2008 Spectroscopy of Organic Compounds Lecture 3 –Infrared and Mass Spec.](https://reader036.fdocuments.us/reader036/viewer/2022081515/5697bfad1a28abf838c9c0d6/html5/thumbnails/18.jpg)
OH
MW = 88
C5H12O
Mass Spectrum of 2-methyl-2-butanol
59
73
70
43
Me
OH OH
55
OH OH
![Page 19: 11 CHEM 344 Organic Chemistry Lab September 9 th and 10 th 2008 Spectroscopy of Organic Compounds Lecture 3 –Infrared and Mass Spec.](https://reader036.fdocuments.us/reader036/viewer/2022081515/5697bfad1a28abf838c9c0d6/html5/thumbnails/19.jpg)
Fragmentation pattern of 2-methyl-2-butanol
OH
OH OH
- CH2CH3
- H2O
m/ z = 70
OH OH
m/ z = 73
- CH3
Me
m/ z = 55
- CH3
![Page 20: 11 CHEM 344 Organic Chemistry Lab September 9 th and 10 th 2008 Spectroscopy of Organic Compounds Lecture 3 –Infrared and Mass Spec.](https://reader036.fdocuments.us/reader036/viewer/2022081515/5697bfad1a28abf838c9c0d6/html5/thumbnails/20.jpg)
Mass Spectrum of 2-octanone
OC8H16OMW = 128
113
43 OH
58
O
O
via -cleavage
via -cleavageMcLafferty rearragement
[M].+
![Page 21: 11 CHEM 344 Organic Chemistry Lab September 9 th and 10 th 2008 Spectroscopy of Organic Compounds Lecture 3 –Infrared and Mass Spec.](https://reader036.fdocuments.us/reader036/viewer/2022081515/5697bfad1a28abf838c9c0d6/html5/thumbnails/21.jpg)
O
O
+
CH3+O
m/z = 43
m/z = 113
Molecular ion
m/z = 128
-cleavage at a C=O group
C OC O RR Resonance stabilized acylium cation
![Page 22: 11 CHEM 344 Organic Chemistry Lab September 9 th and 10 th 2008 Spectroscopy of Organic Compounds Lecture 3 –Infrared and Mass Spec.](https://reader036.fdocuments.us/reader036/viewer/2022081515/5697bfad1a28abf838c9c0d6/html5/thumbnails/22.jpg)
OH
m/z = 58
+OH
m/z = 128
McLafferty rearrangement of 1-octanone
1-pentene
Carbonyl compound must possess gamma H-atoms to undergo McLafferty rearrangement
Process always eliminates a neutral alkene, hence McLafferty product is a radical cation
αβ
γ
O
OH
HOH
OH+
m/z = 60m/z = 88
McLafferty rearrangement of a carboxylic acid
ethene
![Page 23: 11 CHEM 344 Organic Chemistry Lab September 9 th and 10 th 2008 Spectroscopy of Organic Compounds Lecture 3 –Infrared and Mass Spec.](https://reader036.fdocuments.us/reader036/viewer/2022081515/5697bfad1a28abf838c9c0d6/html5/thumbnails/23.jpg)
Mass Spectrum of Benzamide
105
77
44
O
O
NH2
O
NH2
C7H7NO
MW=121 121
via -cleavagevia -cleavage
[M].+
![Page 24: 11 CHEM 344 Organic Chemistry Lab September 9 th and 10 th 2008 Spectroscopy of Organic Compounds Lecture 3 –Infrared and Mass Spec.](https://reader036.fdocuments.us/reader036/viewer/2022081515/5697bfad1a28abf838c9c0d6/html5/thumbnails/24.jpg)
Mass Spectrum of Toluene
CH3
MW=92
C7H8
92
91
Loss of H.
Benzyl cation???
![Page 25: 11 CHEM 344 Organic Chemistry Lab September 9 th and 10 th 2008 Spectroscopy of Organic Compounds Lecture 3 –Infrared and Mass Spec.](https://reader036.fdocuments.us/reader036/viewer/2022081515/5697bfad1a28abf838c9c0d6/html5/thumbnails/25.jpg)
Tropylium cation
m/z = 91
CH3
HH
H
H
HH
H-H
Toluene radical cation
m/z = 92m/z = 91 common to all alkyl benzenes