(A)
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1. |
The 13C NMR spectrum of 2-methyl-4,5-dihydrofuran (A) is given below. The spectrum was the result of 32 scans with 1 sec. delay between acquisitions and no proton decoupling. |
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(A) |
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i) |
What would happen to the spectrum if 128 scans were accumulated and added together ? |
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ii) |
What would happen to the spectrum if the spectrum was acquired with a long delay (say 300 seconds) between acquisitions? |
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iii) |
What would happen to the spectrum if a small amount of soluble paramagnetic salt was added to the sample prior to acquisition ? |
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iv) |
What would happen to the spectrum if the 1H spectrum was irradiated with broad-band Rf radiation before (but not during) each acquisition ? |
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v) |
Could the 1H NMR spectrum of this molecule be analysed by first order splitting rules? Why? |
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Answer |
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2. |
The 1H free induction decay (FID) below was acquired following a single 45o pulse to a sample of containing two species. The spectrum obtained following Fourier transformation (FT) is given on the right. |
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Describe what would happen to the FID and to the spectrum obtained following FT when: |
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i) |
The pulse angle was doubled. |
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ii) |
The pulse angle was increased by a factor of 4. |
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iii) |
The pulse angle was increased by a factor of 3. |
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iv) |
64 FIDs were accumulated and added together before FT. |
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Answer |
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