Answer
Answer
Answer
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1. |
A series of 1H NMR spectra of a sample of chloroform (CHCl3) is given below. The spectra were acquired using the saturation-recovery method. Describe in detail how the experiment is carried out and how the T1 for the protons in chloroform could be obtained from the set of spectra given below. Answer |
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2. |
In a biological suspension of cells, it is often difficult to distinguish the signals resulting from species inside the cell from those outside the cell. By employing a soluble paramagnetic transition metal complex which cannot permeate the cell wall, devise an experiment to obtain spectra from compounds inside and outside the cells. Answer |
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3. |
An NMR sample contains protons with both relatively short (say 100 ms) and long (say 10 sec) relaxation times. What would be the qualitative appearance of a series of 1H NMR spectra of the sample acquired rapidly (say successively at intervals of 4 seconds)? Answer |
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4. |
What would happen to the T1 values for the protons and widths of the 1H NMR signal in a solution of CH3Br when : |
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i) |
A soluble Fe(III) salt was added to the solution. |
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ii) |
The sample was dissolved in a solvent with a substantially higher viscosity, e.g. an oil |
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iii) |
The solution was scrupulously deoxygenated before the spectrum was acquired. |
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iv) |
The solution was cooled to near its freezing point. |
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5. |
The 1H NMR spectrum of an organic molecule is usually sharp with resonances which have lines < 0.3 Hz wide. A 2H NMR spectrum of the same sample typically has resonances which are significantly broader with lines approximately 1 Hz (or more) in width. Rationalise this difference. Answer |
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6. |
The 13C NMR spectrum of toluene (CH3C6H5) is given below. The spectrum was the result of 1024 acquisitions added together and was obtained with continuous broad-band proton decoupling. |
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i) |
The intensities of the signals are all different; what factors may be responsible for this ? |
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What measures could you take in order to accurately integrate the spectrum ? |
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