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Semester 2 Examinations 2010 / 2011
Exam Code(s) 4BS2
Exam(s) Bachelor of Science (Hons.)
Module Code(s) CH433
Module(s) Inorganic Chemistry II
Paper No. I
External Examiner(s) Professor K. Molloy
Internal Examiner(s) Dr. T. Higgins , Dr. P. O'Leary
Answer 4 questions. Answer one question from each of Sections A and B and two questions from Section C.
No. of Pages 5 Following this page
Course Coordinator Dr. A. Erxleben
Requirements log tables with periodic table
Section A Answer one question from this section.
1. Answer each of the following: Describe in some detail the oxidation of hydrocarbons by iron containing enzymes. In your answer pay particular attention to the following; (a) The significance of these enzymes in biological systems. [20 marks] (b) An overview of the main features of a typical catalytic cycle. [30 marks] (c) The role(s) of oxygen. [20 marks] (d) The role(s) of iron. [30 marks]2. Answer each of the following: Describe in some detail how the mechanisms of action of the enzymes thermolysin and carboxypeptidase A have been studied. In your answer pay particular attention to the following; (a) The reaction catalysed and the nature of the active sites of these enzymes. [20 marks](b) The key features of the hydrolytic mechanism. [30 marks](c) The historical development of ideas on the nature of the catalysis. [20 marks] (d) Key experimental evidence that influenced proposals on the mechanism of
catalysis. [30 marks] more on the next page
Section B Answer one question from this section.
3. Answer each of the following: (a) In the complexes below complete an electron count and calculate the oxidation
state of the metal. In each case explain how you have reached your answer.
[3 x 12 marks] (b) Using crystal field theory describe the formation of octahedral complexes of
transition metals. In your answer explain why Fe(II) has a strong preference for octahedral geometry with a low spin. Under what circumstances might it have a high spin? [50 marks]
(c) Outline situations where β-Hydride elimination from organometallic compounds
is not possible. [14 marks] 4. Answer each of the following: (a) There are two common alkene isomerisation mechanisms which may happen with
transition metal complexes. Discuss the mechanisms of and indicate how you might distinguish whether a particular complex favours one mechanism over the other. [50 marks]
(b) The hydroformylation reaction (below) mechanism consists of the following
Oxidative addition of hydrogen to rhodium, co-ordination of the alkene, hydrometalation, co-ordination of CO, migratory insertion, oxidative addition and reductive elimination. Draw out the catalytic cycle showing the species involved at each stage remembering to provide the alternate routes to the two possible products. Also discuss what is happening at each stage of the catalytic cycle.
[50 marks] more on the next page
Section C Answer two questions from this section.
5. Answer each of the following:Read the following paragraph and consider the figure that accompanies it, both taken from the literature#. Answer the questions that follow. “As part of the continuing X-ray crystallographic studies of carboxypeptidase A (CPA) and its interaction with inhibitors and substrates, we now report the structure of the complex between CPA and the slowly hydrolysed substrate N-benzoyl-L-phenylalanine (BZF). More properly, the structure (Figure 2) observed at room temperature as well as slightly subzero temperature is that of an enzyme- substrate-product complex. The structure also represents an enzyme-product complex for the hydrolysis of N-benzoyl-L-phenylalanine-L-phenylalanine (BZF-F) and may depict the “Michaelis complex” for the reverse, synthetic reaction.”
# J. Am. Chem. Soc., Vol 109, No 18, 1987 5537
(a) Explain the terms, substrate, inhibitor, enzyme-substrate-product complex, enzyme-product complex and Michaelis complex as used in the text. Draw structures for the molecules BZF and BZF-F mentioned in the text.
[20 marks] Question continued on the next page
(b) Show that you understand the implications drawn by the authors for the mechanism of peptide hydrolysis. [20marks]
(c) Critique this work in the context of other studies on zinc catalysed hydrolysis. [10marks]6. Answer each of the following: Read the following paragraph taken from the literature#. Answer the questions that follow. “Triplet dioxygen reacts with ferrous cytochrome P450cam with a second-order rate constant of 1.7 × 106 M-1 s-1 to produce a stable dioxygen adduct (Kaff = 106 M-1). One electron from the iron(II) center and one from the triplet oxygen pair create an iron(III)−oxygen bond. This oxygen−iron complex (intermediate D) is relatively stable but can dissociate to an iron(III) and superoxide anion with a rate constant of 0.01 s-1 at room temperature. Within the enzyme, the release of superoxide is followed by its disproportionation and generation of hydrogen peroxide, a source of harmful hydroxyl radicals. Such a step is called the “decoupling reaction” (or “uncoupling reaction”) in the vocabulary of P450 enzymology. The uncoupling reaction is more common in microsomal P450s than with bacterial enzymes. So, the intermediate D has to be regarded as an η1-superoxide ion coordinated to an iron(III) center with an unpaired electron on the terminal oxygen atom. An O−O stretching vibration has been observed at 1141 cm-1 in the resonance Raman spectrum of P450cam under catalytic conditions. The Fe−O−O bending mode has been observed at 401 cm-1 (for the Fe−O) by resonance Raman spectroscopy with an angle of approximately 125−130°.” # Chem. Rev., 2004, 104 (9), pp 3947–3980
(a) Explain the terms, triplet dioxygen, superoxide, peroxide, and hydroxyl radical. [20 marks](b) Draw a structure for D and give your understanding of the chemistry described in
this paragraph. [20 marks](c) Relate this paragraph to the wider context of monoxygenase chemistry and
biology. [10 marks] more on the next page
7. Answer each of the following:
O Ph Ph
(i) BuLi, THF -78oC, 10 Min (ii) PropylBr
O PhPr Pr
OH PhPr Pr
The diagram above shows a synthetic scheme. In each question below explain your reasoning. (a) Suggest a reagent A to carry out the first step. How might this reagent be
prepared? [15 marks] (b) What is the structure of B? [10 marks] (c) When B is alkylated as shown what reagents and conditions C should be used? [15 marks] (d) What reagents and conditions D should be used to effect the final transformation? [10 marks] 8. Answer each of the following: (a) Predict the order of reactivity of the following in oxidative addition of HCl
(explain your reasoning) A, IrCl(CO)(PPh3)2, B, IrCl(CO)(PMe3)2, C, IrMe(CO)(PMe3)2, D, IrPh(CO)(PMe3)2.
[20 marks] (b) How would you expect the (CO) frequencies of A-D to differ? [20 marks]
(c) What would you expect to see in terms of the (CO) frequencies once the
oxidative addition has occurred? [10 marks]