Identification of Organic
Compounds by GC/MS, IR &
NMR
Marcela James
Overview
• Before Staring…
• GC/MS
– Definition, procedure
– GC/MS for organic unknown
• Infrared
– Definition, procedure
– Infrared for organic unknown
• Molecular Formula
• NMR
– Definition, procedure,
– NMR for organic unknown
• Organic Unknown Identity
• References
• Questions
Before Staring…
• Industry: Team work
• Processes: Identify subproducts
• Is the compound pure?
– Run a GC, only one major peak
• Is ultimate analysis available?
– %C
– %H
– %N
– %S
– %P
– %Halogens
http://ec.europa.eu/environment/chemicals/images/chemicals.jpg
Gas Chromatography
Mass Spectrometry
• Finds molecular weight
• Separation on mass/charge ratio
• Mass/charge “unit” is recorded as a
spectrum
• Types of GC/MS
– Electron Impact Ionization
– Chemical Ionization
http://www.hood.edu/images/content/academics/instruments.JPG
Gas Chromatography
Mass Spectrometry
• Is the parent ion peak present?
– Last important peak
• Halogens or sulfur present?
– Look at M+2 peaks
• Nitrogen present?
– Odd molecular weight
• Common fragmentations?
15 CH3
18 H2O
28 CH2=CH2
46 NO2
77
92
-CH3
GC Organic Unknown
Abundance
18000000
6.84
16000000
14000000
12000000
10000000
8000000
6000000
4000000
2000000
0
Time (min)
6
6.2
6.4
6.6
6.8
7
7.2
7.4
7.6
MS Organic Unknown
Abundance
4.5E+06
4.0E+06
106
3.5E+06
CH3-
3.0E+06
-NH
107
Parent Ion Peak
There is presence
of Nitrogen
2.5E+06
2.0E+06
1.5E+06
1.0E+06
5.0E+05
0.0E+00
m/z
0
CH3
15
28
13
10
39
20
30
77
CH2=CH2
40
52
50
60
91
65
70
80
90 100 110 120
Infrared Spectroscopy
• Identifies functional groups
• Infrared region from 13000cm-1 to
40cm-1
• Liquids in sodium chloride cells
• Solids in:
– Solution with solvent
– Nujol mull (mineral oil)
– KBR solid disk
http://www.chem.tsukuba.ac.jp/teranisi/images/apparatus/FTIR.jpg
Infrared Spectroscopy
• Is a carbonyl group present? (18201660cm-1)
If present look for:
– Acids, OH (3400-2400cm-1)
– Amides, N-H (~3400cm-1)
– Esters, C-O (1300-1000 cm-1)
– Anhydrides, C=O (1810-1760cm-1)
– Aldehydes, C-H (2859 & 2750cm-1)
– Ketones, eliminate previous five
choices
Infrared Spectroscopy
• IF carbonyl (C=O) is absent:
– Alcohols, O-H (3400-3300cm-1)
– Amines, N-H (~3400cm-1)
– Ethers, C-O (1300-1000cm-1)
• Double Bonds, Aromatic Rings:
– Double bond C=C, (~1650cm-1)
– Aromatic, C=C (1600-1450cm-1)
http://www.ewels.info/img/science/molecules/benzene.jpg
IR Organic Unknown
Transmittance
120
110
100
No carbonyl
90
80
70
C-H aromatic
60
C-CH3 methyl
50
40
N-H amine
30
C=C ring stretch
20
10
0
3900 3500
Wavenumber
3100 2700 2300
1900 1500
1100
700
Molecular Formula
• Organic compound definitely has:
– A nitrogen (as an amine)
– A ring (aromatic)
– A molecular weight of 107
• Possible molecular formulas:
– C6H7N2
– C7H9N
• Double Bond Equivalent:
– DBE= C - H/2 + N/2 - X/2 + 2
– DBE= 7- 4.5 + 0.5 +2 = 4
For the 3 double
bonds and the
ring structure
Nuclear Magnetic Resonance
• Locations of carbons and hydrogens
• Sample absorbs electromagnetic
radiation
• Solvent peaks appear in the NMR
spectra
• Species have to be magnetically
active:
– 13C instead of 12C
– 1H instead of 2H
http://www.pharmacy.arizona.edu/yanglab/NMRFacility/NMR.JPG
1H
NMR
•Solvent peaks:
–TMS: (Si(CH3)4) 0ppm
–Chloroform: (CDCl3) 7.2ppm
–Acetone: 2.1ppm
•Look for obvious chemical shifts:
12
O-CH3
X-C-H
-C C-H
O
-COOH
-C-H
-H
C=C-H
7
6
N-H
CH3
0
12
11
10
9
8
5
4
3
2
1
0
ppm
1H
NMR for Organic Compound
CH3
H
H
NH2
H
H
13C
NMR
• Solvent Peaks:
– Dichloromethane: (CHDCl2) 53ppm
– Chloroform: (CDCL3) 77ppm
– Acetone: (C3OH6) 205ppm
• Look for obvious chemical shifts:
12
-C=CO
O
-C-H
-C-OH
-C C-
C-Cl, C-Br
CH2
-C-O-
CH3
0
220
200
180
160
140
120
100
80
60
40
20
0
ppm
13C
NMR Organic Compound
1
6
6
2
5
3
2
4
5
4
3
1
C-CH3
C-NH2
CH3
The Organic unknown is…
NH2
CH3
• m-Toluidine
• m-Aminotoluene
• ρ=107.17 g/mol
• BP: 203°C
• Carcinogen
One million pounds produced
annually in the U.S.
References
• Silvertein Robert M. Webster, Francis X.
Kiemle, David J. Spectrometric
Identification of Organic Compounds,
2005. State University of New York. John
Wiley and Sons
• Spectral Database for Organic Compounds
(SDBS), National Institute of Advance
Industrial Science and Technology (AIST),
Japan. Website:
Questions
?
?
?
?
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