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1. |
The metacyclophane (1) was reported in 1987 (J. Amer. Chem. Soc. 1987, 109, 6878). In the 1H NMR spectrum of this molecule, the methine hydrogen occurs at d -4.03 ppm. Given that the methine proton of 4-propylheptane occurs at d 1.2 ppm, estimate the position of the methine proton in (1). |
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2. |
In the complex 3-dimensional structure of a protein, groups are held in relatively fixed positions by hydrogen bonding. Amino acids with aromatic rings such as tyrosine and phenylalanine often influence the chemical shifts of groups which are constrained nearby (a ring current effect). Given that the 1H chemical shift of the CH3- group of free alanine (CH3CHNH3+COO-) is d 1.22, estimate the chemical shift if it were constrained: |
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i) |
2.8 Å above the centre of the aromatic ring of a phenylalanine residue. |
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ii) |
3.8 Å above the centre of the aromatic ring of a phenylalanine residue. |
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iii) |
In the plane of the aromatic ring but displaced 4.9 Å from the centre of the ring. |
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3. |
In a sample of CH2Cl2, the 13C NMR spectrum is an obvious triplet and the 1H NMR spectrum a strong singlet. Rationalise the appearance of the spectra. |
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4. |
The 1H and 31P NMR spectra of trimethyl phosphate, (CH3O)3PO, are given below. Rationalise the appearance of both spectra. |
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