9. NMR

Fill out the following table:

Calculate the Larmor frequency for 1 H and 13 C for an external magnetic field B(0) of 9.4 Tesla and 14.1 Tesla, respectively.

Consider a spin system of four protons H(A), H(B), H(C) and H(D) with chemical shift values of

d(H(A))=0.1 ppm

d(H(B))=0.4 ppm

d(H(C))=7.0 ppm

d(H(D))=7.1 ppm

Protons A and C are coupled to each other with J(AC)=10 Hz, likewise, protons B and D are coupled to each other with J(BD)=10 Hz.

Analyze the spectrum of protons C and D when measuring at either 100,200 or 400 MHz by calculating the difference of Larmor frequencies of H(C) and H(D) and then qualitatively drawing their NMR spectra.

Explain qualitatively why exercise 3 would have been much more difficult for a two spin system with d(H(A))=7.0, d(H(B))=7.1 and J(AB)=10 Hz?

Which of the following molecules belongs to the 1 H NMR spectrum shown below? Please assign all resonances. Explain in one sentence why you can rule out the other proposed structures.

Note: The peak at 7.27 ppm is caused by the solvent and can be ignored.

Draw the structure of alanine and histidine and use the chemical shift reported in the table to draw the 1 H 1 D NMR spectrum.

Consider also J coupling qualitatively.

The Figure below shows the structure of arginine at pH 7 along

with pH dependent (from pH = 7 to ca. 14) 13 C and 15 N chemical shift data of arginine (solid black dots).

a) Which pH dependent reactions are observed?

b) Assign each resonance to an atom in the given structure based on their chemical shifts and pH dependence.

Why can utilization of para-CF3 labelled phenylalanine (Phe) be advantageous compared to para-F labelled phenylalanine? What labelling strategy would you propose for introducing para-CF3-Phe and para-F-Phe, respectively?

Many pharmaceuticals contain fluorine nuclei. Explain briefly how you could use 19F NMR to study the interaction between such a pharmaceutical and its target protein. Why wouldn’t the same approach work using 1H NMR?

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