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1. |
Due to elements of symmetry within the structure of the molecule, the 13C NMR spectrum of ethane contains only a single resonance, the corresponding spectra of (CH3)2CHBr and (CH3)3CBr would contain 2 resonances. How many distinct resonances are there in :
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i) |
The 1H NMR spectrum of (CH3)4C ? |
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ii) |
The 13C NMR spectrum of (CH3)4C ? |
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iii) |
The 31P NMR spectrum of (CH3CH2)3PO ? |
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iv) |
The 13C NMR spectrum of (CH3CH2)3PO ? |
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v) |
The 1H NMR spectrum of (CH3CH2)3PO ? |
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vi) |
The 29Si NMR spectrum of (CH3)3SiSi(Et)3 ? |
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vii) |
The 1H NMR spectrum of (CH3)3SiSi(Et)3 ? |
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viii) |
The 13C NMR spectrum of (CH3)3SiSi(Et)3 ? |
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Answer |
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2. |
Dispersion is a term used to express the notion of how well resonances in an NMR spectrum are separated from one another (in Hz) - it is a qualitative term expressing the ease with which signals can be distinguished. Two signals occur at 2.1 and 2.3 ppm in the proton spectrum in a spectrometer operating at 200 MHz for 1H. |
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i) |
What is the frequency difference between the resonances in Hz? |
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ii) |
What is their frequency difference (in Hz) in a spectrometer operating at 600 MHz for 1H observation? |
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iii) |
For a given type of nucleus, what is the general relationship between "dispersion" and the magnetic field strength of the NMR spectrometer? |
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Answer |
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3. |
The chemical shift scale on a NMR spectrum is typically given in dimensionless units termed "parts per million" (ppm) from some reference compound. What is the relationship between a chemical shift scale in Hz. and a scale in "ppm" ? Answer |
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4. |
In NMR spectrometers commonly used in medicine, the resonance frequency for the protons in water is 60MHz. If such an instrument was to be used to observe 31P, what frequency of Rf. radiation would be required ? Answer |
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5. |
In a magnetic field of strength 2.349 T, the resonance frequency of 15N nuclei is 10.13 MHz. What is the resonance frequency of 15N in a magnet of 11.745T ? Answer |
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6. |
The magnetogyric ratio of the deuterium (2H) nucleus is approximately 6.5 times smaller than that of the proton. In a magnet where a 1H spectrum can be observed at about 400 MHz, what is the approximate frequency of Rf. radiation you would need to observe the 2H NMR spectrum ? Answer |