Lecture 9 - NMR spectroscopy 1 TODAY 1. 1. 2. 3. Intro to...

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NMR spectroscopy 1
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TODAY Intro to NMR (Slides 3 – 10). Three fundamental NMR Parameters: 2 1. Chemical shift (ppm scale) 2. Intensity information 3. Nearest neighbour analysis Problem Solving
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The World’s Premier Antifungal Drug How is the structure of this molecule determined? 3
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1 H NMR spectrum of Amphotericin B methyl ester (Professor Jeff Manthorpe) The structure of amphotericin B is determined by NMR ! 4 Spectrum obtained for Professor Jeff Manthorpe
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NMR in CONTEXT: Information on molecular structure is typically obtained using ~ 4 routine spectroscopic methods: 1. UV-Vis (for conjugated systems). 5 2. IR (for certain functional groups). 3. Mass spectrometry (MS) (for molecular weight and the weight of fragments). C n H m OSNX 4. Nuclear magnetic resonance (NMR) gives detailed structural information (including Stereochemistry). O OH O H
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Organic Chemists mainly rely on two methods of NMR analysis 1 H (proton (hydrogen) NMR) 13 C (carbon NMR) – Note: 12 C nuclei not detected by NMR 6 • Also possible to detect: 19 F, 14 N, 17 O, 2 H (D), 31 P *NMR observable nuclei have odd mass or odd atomic number, or both
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NMR “experiment” • In the presence of an applied magnetic field (B), NMR-active nuclei (e.g. 1 H) align their magnetic moment vectors ( μ ) with or pposed the field. 7 opposed to the field. B μ or This generates two spin states E 10 6 10 6 + 1 Small excess in lower state
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NMR instrument Spin 8 Note: MRI - magnet rotates; Sample is stationary
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Generate a 1 H or 13 C spectrum Intensity Observe Absorption of Rf energy ( E) E 9 B lo B hi B (magnetic field strength)
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E α B (Bloch equation) We have to select the proper 10 E (MHz) B (magnetic field strength) magnetic field strength to observe spin flip and the absorption of Rf energy (resonance). Rf frequency ( E) is fixed and the magnetic field strength is varied. B hi B lo
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Three fundamental NMR Parameters give useful structural information 1. Chemical shift (ppm scale) – gives 11 functional group information. 2. Intensity information – how many
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Lecture 9 - NMR spectroscopy 1 TODAY 1. 1. 2. 3. Intro to...

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