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Chem 3al lecture for NMR #2

Chem 3al lecture for NMR #2 - Spin-Spin Splitting(J...

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Spin-Spin Splitting ( J Coupling) Coupling of spins provides connectivity information about neighboring nuclei
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6ppm 5ppm 4ppm 3ppm 2ppm 1ppm 0 ppm TMS 1 H NMR Spectrum of 1,1,2-trichloroethane Cl H A Cl Cl H B H B H A H B Observed! 6ppm 5ppm 4ppm 3ppm 2ppm 1ppm 0 ppm TMS Predicted
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J Coupling Local magnetic fields of nuclei are influenced by the local magnetic fields of neighboring, nonequivalent nuclei Review: When spin ½ nuclei are placed in an external magnetic field, they align into two spin states, alpha and beta. The alpha spin state is aligned with the field and any influence exerted by such nuclei will be opposite from those in the beta state whose field is aligned against the external field.
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H A ’s Influence on H B where H B would be with no J coupling 4ppm Cl H A α Cl Cl H B H B resonance due to H A 's influence on both H B 's resonance due to H A 's influence on both H B 's J AB = 6.0 Hz a doublet (d) 3.9 (d, 2H, J AB = 6.0 Hz) Cl H A β Cl Cl H B H B Cl H A Cl Cl H B H B
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H B ’s Influence on H A 6 ppm 5.5 ppm where H A would be with no J coupling Cl H A Cl Cl H B α H B α resonance due to H B 's influence on H A resonance due to H B 's influence on H A Cl H A Cl Cl H B β H B β Cl H A Cl Cl H B β H B α Cl H A Cl Cl H B α H B β a triplet (t) 5.8 (t, 1H,
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