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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 ChromatographyMass 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 ChromatographyMass 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 H2O28 CH2=CH2
46 NO2 7792 -CH3
GC Organic Unknown
0
2000000
4000000
6000000
8000000
10000000
12000000
14000000
16000000
18000000
6 6.2 6.4 6.6 6.8 7 7.2 7.4 7.6
6.84
Time (min)
Abundance
MS Organic Unknown
0.0E+00
5.0E+05
1.0E+06
1.5E+06
2.0E+06
2.5E+06
3.0E+06
3.5E+06
4.0E+06
4.5E+06
0 10 20 30 40 50 60 70 80 90 100 110 120
Abundance
m/z
15
13
28
39 52 65
7791
106107
CH2=CH2CH3
Parent Ion PeakThere is presence of Nitrogen
-NHCH3-
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? (1820-
1660cm-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
0
10
20
30
40
50
60
70
80
90
100
110
120
70011001500190023002700310035003900
Transmittance
Wavenumber
C-H aromatic
N-H amine
No carbonyl
C=C ring stretch
C-CH3 methyl
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:
0
12
0123456789101112 ppm
CH3N-HC=C-H-H-C-H
O
-COOH
O-CH3 X-C-H -C C-H
1H NMR for Organic Compound
CH3
NH2
H
HH
H
13C NMR• Solvent Peaks:– Dichloromethane: (CHDCl2) 53ppm
– Chloroform: (CDCL3) 77ppm
– Acetone: (C3OH6) 205ppm
• Look for obvious chemical shifts:
0
12
020406080100120140160180200220
ppm
CH3-C-O--C-OH
O
-C=C-
-C-H
O
CH2
-C C- C-Cl, C-Br
13C NMR Organic Compound
CH3
C-NH2
C-CH3
5
6
12
3
4
13
5
6 4
2
The Organic unknown is…
• m-Toluidine
• m-Aminotoluene
• ρ=107.17 g/mol
• BP: 203°C
• Carcinogen
NH2
CH3
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
??
??
http://www.wpclipart.com/cartoon/more_cartoons/Mad_scientist.png
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