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

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