CH3D3 Revision Workshop 2013-14 PDF

CH3D3 Revision Workshop 2013-14 1. Explain what is meant by secondary electrostatic interactions in the context of hydrogen bonded complexes. [10%] 2. In the scheme below identify compounds A and B. In chloroform, compound B has an apparent Mn by vapour pressure osmometry (VPO) of 830 a.m.u. Propose...

CH3D3 Revision Workshop 2013-14 1. Explain what is meant by secondary electrostatic interactions in the context of hydrogen bonded complexes. [10%] 2. In the scheme below identify compounds A and B. In chloroform, compound B has an apparent Mn by vapour pressure osmometry (VPO) of 830 a.m.u. Propose a reasonable mode of supramolecular assembly of compound B. [20%] NH2 O C13H27 H2N O OCH2CH3 NCO NH C18H34O3 B A Pyridine Ethanol C17H31N3O Mn (VPO) = 830 +/- 10 Molecular mass (electron impact mass spectrometry) = 412 3. (a) Sketch the supramolecular 1:1 complex you would expect to form upon mixing 7 and 8 in a non-polar solvent. [5%] (b) Estimate the expected change in free energy upon formation of this complex in chloroform at 298K and hence state whether this pair would be useful as a structural element in supramolecular chemistry. How does this change if a molecule of each contained two of the same functional groups? [25%] You may require the following information for your calculation: ΔΔGHB = -(α-αs)(β-βs)+6 kJmol-1 β for 7 = 9.9 β for 8 = 7.8, α for 8 = 2.9 α for chloroform = 2.2 β for chloroform = 0.8 R = 0.008314 kJ K-1 mol-1. where α and β are normalised hydrogen bond functional group donor and acceptor constants respectively. 4. Explain briefly what is meant by the hydrophobic effect and why it is important in the folding of soluble, globular proteins. [15%] 1 5. A series of β-cyclodextrins, represented schematically below, substituted with either a hydroxyl (R = OH) or a protonated amine (R = NH2+Me) were investigated as host molecules in water for the binding of aromatic catecholate guests 1 and 2. The free energy of formation of the complexes, ΔG, was measured in order to find the free energy of ion pairing ΔGion-pair between the doubly deprotonated catecholate 1 and protonated cyclodextrin amine (R = NH2+Me). (a) Draw a schematic for each complex, highlighting and explaining the key interactions responsible for its formation. [30%] (b) By constructing a ‘double mutant cycle’- or thermodynamic cycle find the free energy of ion pairing between the anionic catecholate and cationic cyclodextrin (R = NH2+Me). [30%] (c) Why do you think it was necessary to use the carboxylate in these experiments rather than the neutral carboxylic acid? [10%] (d) Give details of an experiment that might have been used to measure the free energy of formation of the complexes. [20%] (e) Suggest an experiment to verify the supramolecular structure of any of the complexes. [10%] O O O OH O OH O OH catecholate 1, ΔG = -11.5 kJmol-1 for R = OH catecholate 2, ΔG = -12.9 kJmol-1 for R = OH catecholate 1, ΔG = -21.8 kJmol-1 for R = NH2Me catecholate 2, ΔG = -14.3 kJmol-1 for R = NH2Me 2