Identification of Organic Compounds by GCMS IR NMR
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 CH 3 18 H 2 O 28 CH 2=CH 2 46 NO 2 77 92 -CH 3
GC Organic Unknown Abundance 6. 84 Time (min)
MS Organic Unknown Abundance 106 CH 3 - -NH 107 Parent Ion Peak There is presence of Nitrogen CH 3 15 13 m/z 28 77 CH 2=CH 2 39 52 65 91
Infrared Spectroscopy • Identifies functional groups • Infrared region from 13000 cm-1 to 40 cm-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 -1660 cm -1) If present look for: – Acids, OH (3400 -2400 cm-1) – Amides, N-H (~3400 cm-1) – Esters, C-O (1300 -1000 cm-1) – Anhydrides, C=O (1810 -1760 cm-1) – Aldehydes, C-H (2859 & 2750 cm-1) – Ketones, eliminate previous five choices
Infrared Spectroscopy • IF carbonyl (C=O) is absent: – Alcohols, O-H (3400 -3300 cm-1) – Amines, N-H (~3400 cm-1) – Ethers, C-O (1300 -1000 cm-1) • Double Bonds, Aromatic Rings: – Double bond C=C, (~1650 cm-1) – Aromatic, C=C (1600 -1450 cm-1) http: //www. ewels. info/img/science/molecules/benzene. jpg
IR Organic Unknown Transmittance No carbonyl C-H aromatic C-CH 3 methyl N-H amine C=C ring stretch Wavenumber
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= 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: – 13 C – instead of 12 C 1 H instead of 2 H http: //www. pharmacy. arizona. edu/yanglab/NMRFacility/NMR. JPG
1 H NMR • Solvent peaks: –TMS: (Si(CH 3)4) 0 ppm –Chloroform: (CDCl 3) 7. 2 ppm –Acetone: 2. 1 ppm • Look for obvious chemical shifts: O-CH 3 X-C-H -C C-H O -COOH -C-H -H C=C-H N-H CH 3 ppm
1 H NMR for Organic Compound CH 3 H H NH 2 H H
13 C NMR • Solvent Peaks: – Dichloromethane: (CHDCl 2) 53 ppm – Chloroform: (CDCL 3) 77 ppm – Acetone: (C 3 OH 6) 205 ppm • Look for obvious chemical shifts: -C=CO O -C-H -C-OH -C C- -C-O- C-Cl, C-Br CH 2 CH 3 ppm
13 C NMR Organic Compound 1 6 6 2 5 3 2 4 5 4 3 1 C-CH 3 C-NH 2 CH 3
The Organic unknown is… NH 2 CH 3 • 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 ? ? http: //www. wpclipart. com/cartoon/more_cartoons/Mad_scientist. png
- Slides: 20