5_46_l02 - Information Content Available Through NMR We...

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Information Content Available Through NMR
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We need to measure the NMR signals…
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Tetramethylsilane (TMS) is our reference for 1 H, 13 C and 29 Si. The chemical shift (denoted δ ) varies in different chemical environments. δ = [ ( ν obs ν TMS ) / ν TMS ] x 10 6
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Chemical shifts depend on the electronegativities of nearby atoms
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Having 2n+2 π electrons in a ring allows for charge circulation Image courtesy of the U.S. Geological Survey
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We also want to know how much of each signal we have
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NMR provides information on the relative amounts of chemically distinct molecular sites (integrals and intensities)
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Quantitation requires… • Waiting five times the longest spin-lattice relaxation time T 1 M z (t) = M 0 [1 - exp (-t / T 1 )] • The absence of any enhancement, such as that arising from decoupling η = γ X / (2 γ A )
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1 H 1-D integration
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13 C spectra provide useful intensity information
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Image courtesy of U.S. Air Force
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This note was uploaded on 11/27/2011 for the course CHEMICAL E 20.410j taught by Professor Rogerd.kamm during the Spring '03 term at MIT.

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5_46_l02 - Information Content Available Through NMR We...

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