13-NMRHLSF07

13-NMRHLSF07 - at HIGHER chemical shift values . If H...

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NMR Nuclear Magnetic Resonance
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•Extremely useful for determining: • Functional groups •Symmetry •Specific connectivity •Possible on tiny amounts of sample necessary (<1 mg) •Typical sample ~20 mg •Non-destructive
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Basic Theory 1 H and 13 C spin 1/2 = NMR active 2 H(D), 12 C not spin 1/2 = NMR inactive Want to know more? p-chem is for you! A nuclei is charged and spinning and thus creates its own magnetic field.
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The energy difference between the parallel and the antiparallel orientation of the spin in the field is proportional to the strength of the applied magnetic field. ! -spin state " -spin state B o #$ p ! -spin state " -spin state h % = #$ p "spin-flip" Pulse with radiowaves Pulse stops "relaxation" ! -spin state " -spin state + energy detected The NMR Experiment
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Not all H resonate at same frequency - leads to different Chemical Shifts If H surrounded by low electron density (near electronegative group) - deshielded - experiences more of the actual magnetic field - appears
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Unformatted text preview: at HIGHER chemical shift values . If H surrounded by high electron density (near Si) - shielded-experiences less of the actual magnetic field - appears at LOWER chemical shift values . Basic Chemical Shift Values - Table from Loudon provided on Exam Quick check? Which spectra corresonds to iodopropane and which to chloropropane? C 2 H 4 Cl 2 3H 1H 3H can orient their spins in such a way that all three spins produce fields which are parallel to the applied field, two are parallel and one antiparallel, one is parallel and two antiparallel, or all three spins oppose the applied field. There is only one possibility for the first and last of these options, but there are three possibilities for the second and third of these options. H 3 C C H Cl C O OH C C H H C O OH H H Cl C 3 H 6 Br 2 C 7 H 14 O 2 IR (cm-1 ) = 1740 3H 6H 2H 2H 1H C 9 H 10 O C 8 H 10 O...
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This note was uploaded on 05/13/2010 for the course CHEM 151L taught by Professor Roy,christopher during the Fall '08 term at Duke.

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13-NMRHLSF07 - at HIGHER chemical shift values . If H...

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