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Chem-805 Identification of organic and inorganic compounds by spectroscopy

Chem-805 Identification of organic and inorganic compounds by spectroscopy. Mass Spectrometry NMR Infrared. Introduction: Structure Determination. Need information on: Molecular Formula Functional groups Carbon Connectivity Position of substitution on the carbon framework

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Chem-805 Identification of organic and inorganic compounds by spectroscopy

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  1. Chem-805Identification of organic and inorganic compounds by spectroscopy Mass Spectrometry NMR Infrared

  2. Introduction: Structure Determination • Need information on: • Molecular Formula • Functional groups • Carbon Connectivity • Position of substitution on the carbon framework • Stereochemical properties including Dynamic and static aspects.

  3. Characteristics of different Spectrometric methods 1H-NMR 13C-NMR MS IR Scale 0-15 ppm 1-220 ppm 50-4000 amu 400-4000 cm-1 Sample 1-2 mg 10-20 mg < 1 mg < 1 mg Molecular formula Partial Partial Yes No Functional group ~ yes ~ yes limited Yes yes yes yes Very limited Substructure yes yes No Very limited C-Connection Stereochem. & regiostereo-chemistry yes yes No Very limited

  4. Electromagnetic spectrum E kJ/mol 105 103 101 10-1 10-3 10-5 10-7 l cm 10-8 10-6 10-4 10-2 1 102 104 Radio wave: Nuclear Spin transition UV: Electron. transition IR: vibration g Rays X-Rays Microwave: rotation motion UV Visible 200 nm 400 nm Blue 800 nm Red n, cm -1 10000 1000 100 Near IR Middle IR Far IR 1 10 100 l, m

  5. Relationships Photon energy: e =h n=h c /l Energy per Mol: E = N h c /l Where: h =Plank’s constant = 1.58 10-37 kcal sec = 6.63 10-34 J sec c = 3 1010 cm/sec N = Avogadro’s Number = 6.023 1023 l = Wavelength (cm) Energy per Mol: E = 1.20 10-2/l (cm) kJ/mol 2.86 10-3 /l (cm) kcal/mol

  6. Time Scale for structural techniques Technique Approximate time scale (seconds) Electron Diffraction 10-20 Neutron Diffraction 10-18 X-Ray Diffraction 10-18 UV (ultraviolet) 10-15 Visible 10-14 IR (Infra Red) / Raman 10-13 Electron Spin Resonance 10-4 – 10-8 Nuclear Spin Resonance 10-1 – 10-9 Quadrupole Resonance 10-1 – 10-8 Experimental separationof isomers > 102

  7. Determination of structure • First priority:NMR • Provides info on C=O groups • Aromatic / olefinic • Aliphatic • Presence of oxygen (alcohol / ether ..) • Second priority : MS • Help determining molecular formula • Atomic composition • Fragmentation pattern can also help … • Third priority: IR • Identify Functional groups

  8. Functional groups: Unsaturated Benzene Alkene Alkyne Cumulenes Pyridine Imine Nitrile Diazo Isonitrile Oxime Azide Cyanamide

  9. Functional groups Alcohol Thiol Amine Halides (F, Cl, Br, I) Ether Thioether Peroxide Disulfide Hydrazine N-Oxide

  10. Functional groups: carbonyl Aldehyde Ketone Acid Ester Amide Acid derivatives (F, Cl, Br, I) Anhydride Imide

  11. Functional groups: carbonyl Carbonate Thiocarbonate Guanidinium Thioguanidinium Urea Carbamate Thiocarbamate

  12. Functional groups: heteroaromatic, & other Nitro : -NO2 Nitroso : -NO Where Z = O, NH, S Sulfoxide Sulfone

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