CHEM 230 Molecules for Life: Synthesis and Reactivity SEMESTER TWO 2018
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CHEM 230
SEMESTER TWO 2018
CHEMISTRY
Molecules for Life: Synthesis and Reactivity
QUESTION ONE. Answer ALL parts (a) - (d) (20 marks).
(a) Epoxides are useful reactive intermediates which undergo a variety of ring-opening
reactions. They are commonly formed from the reaction of a peracid with an alkene, an example of which is shown below.
(i) Draw a complete mechanism, using curly arrows, for the synthesis of epoxide B from alkene A (2 marks).
(ii) Draw a complete mechanism, using curly arrows, for the conversion of epoxide B
into alcohol C (2 marks).
(iii) Why does alcohol C, prepared using the synthesis described above, have an optical
rotation of 0° (zero degrees)? (1 mark).
Alkene A and epoxide B are achiral molecules. A racemic mixture of alcohol C would be formed. |
(iv) Draw the structure of nitrile D, paying particularly attention to the stereochemistry
of the product (1 mark).
(b) Halogenation of organic molecules can occur in a number of ways. For example, N-
bromosuccinimide undergoes radical reactions. Two reactions are shown below.
(i) Draw the structures of bromide E and bromide F in the boxes above (2 marks).
(ii) What are the names of the three stages of radical reactions? (1 mark).
Initiation, propagation and termination |
(iii) In the synthesis of bromide F, bromine is what type of reagent? (1 mark).
Electrophilic /
(circle one)
/ Nucleophilic
(c) Provide structures for the missing product/s, in the following reactions, paying attention to stereochemistry where appropriate (1 mark each).
(i)
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(ii)
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(5 marks total)
(d) The Diels-Alder reaction and the Claisen Rearrangement are both examples of pericyclic reactions, whereby a cyclic movement of electrons can lead to formation of a new product.
(i) Draw one of the products of the following Diels-Alder reaction. Note that you do NOT need to draw in any stereochemistry on the product (2 marks).
O
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(ii) Compound G can undergo an intra-molecular Diels-Alder reaction. Circle the
structure of the product you would expect to be formed in this reaction (2 marks).
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(iii) Draw the expected product of the following Claisen Rearrangement reaction (1 mark).
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QUESTION TWO. Answer ALL parts (a) - (d) (20 marks).
(a) Complete the following statements (i)-(iv) by circling the appropriate answers (½ mark each, 2 marks total).
In electrophilic aromatic substitution (SEAr) reactions:
(i) Resonance / Induction is based on the electronegativity of the atoms involved.
(circle one)
(ii) Resonance is a stronger / weaker effect than induction.
(circle one)
(iii) The phenoxide ion is more / less able to undergo SEAr reactions than phenol.
(circle one )
(iv) Nitro (NO2) substituents are ortho,para / meta directing.
(circle one)
(b) For (i) and (ii) below, draw the main product(s) of the reactions and state if the reactions
occur faster or slower relative to benzene (5 marks total).
(i)
Reaction occurs at a faster / slower rate, relative to the same reaction with
benzene. (circle one)
(ii)
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Reaction occurs at a faster / slower
benzene. (circle one)
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(c) The following questions (i)-(iv) relate to the reaction scheme below:
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(i) Fill in the reagent(s) for the reaction of amide K in the box provided. (1 mark) (ii) Draw the structure of the azo dye produced in this scheme. (1 mark)
(iii) Why do we convert aniline to amide K for the electrophilic aromatic substitution
(SEAr) reaction? (2 marks)
Amines are highly activating aromatic substituents and a common issue is they often give polysubstituted products for electrophilic aromatic substitution. Amides are less activating (but still activating and ortho/para directors) |
(iv) Draw the arenium ions generated in the formation of the ortho product shown in
the scheme above (2 marks)
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(d) For parts (i) to (iv) below, give the structures of the reagents/products of reactions. Part (v) requires a mechanism to be drawn.
(i)
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(2 marks) (ii)
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(1 mark)
(iii)
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(1 mark)
(iv)
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(1 mark)
(v) Give the mechanism for the formation of cyanohydrin M from ketone L. (2 marks)
O
C |
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H O
CN |
OH
CN |
Page 8 of 18
QUESTION THREE. Answer ALL parts (a) - (c) (20 marks).
(a) Ketones such as ketone N, are versatile building blocks in synthetic chemistry.
(i) Provide the reagents and reaction conditions required for each of the transformations 1, 2 and 3 in the boxes provided (2 marks each, 6 marks total).
2022-10-22