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bcmb8190_a7_10

bcmb8190_a7_10 - τ is shorter 3 The magnitude is simply...

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BCMB/CHEM 8190 Answers, Problem Set 7 1) a) b) Upfield peaks are weaker because the two bond Ni to Ci-1 coupling constant is smaller than the one bond coupling to Ci c) Weaker peaks will not always be upfield – it is coincidence in this case. They just occur at the carbon chemical shifts of the respective alpha carbons. 2a) T 1 /T 2 = 2/3 x ( τ m ω N ) 2 = 750/62 = 2/3 x ( τ m x 2 π x 60 x 10 6 ) 2 => τ m = 11.3 ns 1/T 2 = (dd/4) x 2/5 x S 2 x τ m = 5.85 x 10 9 x 2/5 x S 2 x 1.13 x 10 8 => S 2 = 0.77 2b) (3cos 2 θ -1)/2 = S = 0.8 => 21º 2c) increased internal motion, effective
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Unformatted text preview: τ is shorter 3) The magnitude is simply 94-73 = 11 Hz. The sign is positive. This is because one bond 1 H-15 N couplings are negative because of the negative gamma for 15 N. A decrease in splitting must come from a positive RDC (we assume all RDCs would be less than 94 Hz). 4) Scaling in solids NMR is by a factor of (1-3cos 2 θ )/2 . This factor is zero at 54.7 ° , but 0.12 at 50 ° . The line would be 24 ppms wide or 24 X 500 X 0.25 or 3000 Hz at 125 MHz for 13 C....
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