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i) d 9.5 ii) d 6.9 iii) d 6.0 iv) d 2.2 v) d 1.0 Answer |
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1. |
The simple molecules below contain the NMR-active nuclei 14N (I=1), 31P (I=1/2), 1H (I=1/2) and 13C (I=1/2). Considering only the coupling constants through one bond (1Jax) as being significant, construct diagrams which schematically represent the splitting pattern you would see in : |
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i) |
The 1H NMR spectrum of the ammonium ion [NH4+]. |
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ii) |
The 14N NMR spectrum of the [NH4+]. |
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iii) |
The 13C NMR spectrum of trimethylamine [(CH3)3N] |
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iv) |
The 31P NMR spectrum of phosphine [PH3]. |
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v) |
The 1H NMR spectrum of phosphine [PH3]. |
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vi) |
The 13C NMR spectrum of H2P-CH2-PH2. |
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vii) |
The 13C NMR spectrum of [(PH2)3CH]. |
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Answer |
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2. |
Classify the spin systems to which the protons of the following molecules belong (e.g. A2X2, AA'XX' etc.). Assume that any chemically non-equivalent protons are well separated in chemical shift. |
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i) |
thiophene |
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ii) |
CH3CH2OCH3 |
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iii) |
CH2=CH2 |
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iv) |
m-dibromobenzene |
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v) |
CH2BrCH2Br |
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vi) |
CH2BrCHBrI |
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vii) |
o-dibromobenzene |
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viii) |
p-dibromobenzene |
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ix) |
p-bromotoluene |
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x) |
o-xylene (CH3 groups DO couple to aromatic protons). |
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xi) |
cis-1,2-dichlorocyclopropane |
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xii) |
trans-1,2-dichlorocyclopropane |
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Which of these spin systems could be analysed using first order splitting rules ? Why ? Answer |
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3. |
The protons of the 3-chlorobutyrate ion [CH3CHClCH2CO2-] can be labelled as an A3MXY spin system. |
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i) |
Exactly what information tell you about the spin system? |
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ii) |
Could the 1H NMR spectrum of this molecule be analysed by normal first-order rules ? Why ? |
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Answer
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4. |
The 1H NMR spectrum of (E)-2-pentenal (given below) has 5 distinct resonances: d 9.5 (1H, doublet), d 6.9 (1h, doublet of triplets), d 6.0 (1H, doublet of doublets), d 2.2 (2H, multiplet) and d 1.0 (3H, triplet). Sketch and clearly describe the 1H spectra you would obtain while applying strong Rf. irradiation at : |
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i) d 9.5 ii) d 6.9 iii) d 6.0 iv) d 2.2 v) d 1.0 Answer |
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