Dipolar-Coupling-and-Solids-NMR

Dipolar-Coupling-and-Solids-NMR - Dipolar Coupling and...

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Dipolar Coupling and Solids NMR BCMB/CHEM 8190
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13 C CP-MAS, 30 mg cellulose, 9 min 13 C solution, sat’d glucose, 8 min Liquids v. Solids One can collect similar spectra but some tricks are required
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The Classical Dipole-Dipole Interaction: E = ( μ 0 /4 ! )(( μ 1 · μ 2 )/r 3 – 3( μ 1 · r )( μ 2 · r )/r 5 ) r = i r x + j r y + k r z = i r sin " cos # + j r sin " sin # + k r cos " μ 1 μ 2 r B 0 " x y z " # r
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Quantum Mechanical Dipolar Coupling μ = ( $ h/2 ! )( i I x + j I y + k I z ) = ( $ h/2 ! )f( I z , I +,- ) H D = ( μ 0 $ 1 $ 2 h 2 )/(16 ! 3 r 3 )(A + B + C + D + E + F) A,B,C . . Grouped by type of operator, 0,1,2 Quantum A = - I z1 I z2 (3cos 2 " - 1), B = (1/4)( I +1 I -2 + I -1 I +2 ) (3cos 2 " - 1) ………. . E = -(3/4)( I +1 I +2 )sin 2 " exp(-2i # ), F = ……. .
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To First Order Only I z1 I z2 Term is Important A doublet would result – much like scalar coupling but large: as much as -60,000 Hz for a 13 C- 1 H pair. Splittings are angle dependent – ranging from -60,000 to +30,000. In a solid all possibilities superimpose: The result is a powder pattern Points at 90º on a sphere are most abundant D
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Dipolar-Coupling-and-Solids-NMR - Dipolar Coupling and...

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