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

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

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 CH 3 18 H 2 O 28 CH 2 =CH 2 46 NO CH 3

GC Organic Unknown 6.84 Time (min) Abundance

MS Organic Unknown Abundance m/z CH 2 =CH 2 CH 3 Parent Ion Peak There is presence of Nitrogen -NHCH 3 -

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

Infrared Spectroscopy Is a carbonyl group present? ( cm -1 ) If present look for: –Acids, OH ( cm -1 ) –Amides, N-H (~3400cm -1 ) –Esters, C-O ( cm -1 ) –Anhydrides, C=O ( cm -1 ) –Aldehydes, C-H (2859 & 2750cm -1 ) –Ketones, eliminate previous five choices

Infrared Spectroscopy IF carbonyl (C=O) is absent: – Alcohols, O-H ( cm -1 ) – Amines, N-H (~3400cm -1 ) – Ethers, C-O ( cm -1 ) Double Bonds, Aromatic Rings: – Double bond C=C, (~1650cm -1 ) – Aromatic, C=C ( cm -1 )

IR Organic Unknown Transmittance Wavenumber C-H aromatic N-H amine No carbonyl C=C ring stretch C-CH 3 methyl

Molecular Formula Organic compound definitely has: –A nitrogen (as an amine) –A ring (aromatic) –A molecular weight of 107 Possible molecular formulas: –C 6 H 7 N 2 –C 7 H 9 N Double Bond Equivalent: –DBE= C - H/2 + N/2 - X/2 + 2 –DBE= = 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: – 13 C instead of 12 C – 1 H instead of 2 H

1 H NMR Solvent peaks: –TMS: (Si(CH 3 ) 4 ) 0ppm –Chloroform: (CDCl 3 ) 7.2ppm –Acetone: 2.1ppm Look for obvious chemical shifts: ppm CH 3 N-HC=C-H -H -C-H O -COOH O-CH 3 X-C-H-C C-H

1 H NMR for Organic Compound CH 3 NH 2 H H H H

13 C NMR Solvent Peaks: –Dichloromethane: (CHDCl 2 ) 53ppm –Chloroform: (CDCL 3 ) 77ppm –Acetone: (C 3 OH 6 ) 205ppm Look for obvious chemical shifts: ppm CH 3 -C-O- -C-OH O -C=C- -C-H O CH 2 -C C- C-Cl, C-Br

13 C NMR Organic Compound CH 3 C-NH 2 C-CH

The Organic unknown is… m-Toluidine m-Aminotoluene ρ= g/mol BP: 203°C Carcinogen NH 2 CH 3 One million pounds produced annually in the U.S.

References Silvertein Robert M. Webster, Francis X. Kiemle, David J. Spectrometric Identification of Organic Compounds, 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 ? ? ? ?