Chemistry $^{3}$ : Introducing inorganic, organic and physical chemistry

Andrew Burrows, John Holman, Andrew Parsons

Chapter 18

Isomerism and stereochemistry - all with Video Answers

Educators

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Chapter Questions

Problem 1

The synclinal conformation of 1,2 -dichloroethane is $4.8 \mathrm{~kJ} \mathrm{~mol}^{-1}$ higher in energy than the anti-periplanar conformation. The two energy barriers for rotation about the C-C bond in 1,2 - dichloroethane are $21.5 \mathrm{~kJ} \mathrm{~mol}^{-1}$ and $38.9 \mathrm{~kJ} \mathrm{~mol}^{-1}$ higher than the energy of the anti-periplanar conformation. (Section 18.2)
(a) Sketch a graph of energy versus angle of rotation about the C-C bond (dihedral angle) for 1,2 -dichloroethane.
(b) What conformation of 1,2 -dichloroethane has the highest energy?

RS

Rajesh S.

Numerade Educator

Problem 2

The following questions relate to meso-butane-2,3-diol. (Sections $18.2$ and $18.4$ )
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meso-butane-2,3-diol
(a) Draw sawhorse and Newman projections of the synperiplanar conformation of meso-butane-2,3-diol.
(b) Assign $R$ or $S$ configuration to each of the chiral centres in meso-butane-2,3-diol.
(c) Draw a Fischer projection of meso-butane-2,3-diol and use this to help to explain why this is a meso compound.
(d) Draw a Fischer projection of a diastereomer of mesobutane-2,3-diol.

RS

Rajesh S.

Numerade Educator

Problem 3

The citric acid cycle (Krebs cycle) is a series of reactions involved in the oxidation of fats, proteins, and carbohydrates in the body to form carbon dioxide and water (p.960). One step in the citric acid cycle is the addition of water to fumaric acid to make malic acid. (Sections $18.3$ and 18.4)

RS

Rajesh S.

Numerade Educator

Problem 4

Tetrodotoxin is a potent poison that is found in the puffer fish. It is estimated to be more than 10000 times deadlier than. cyanide ions. The structure of tetrodotoxin contains a group of interconnected 6-membered rings. Which of the bonds on the cyclohexane ring of tetrodotoxin are in an axial position and which are in an equatorial position? (Section 18.2)Mary in Jlapan consider the puffer fish (fugu) a deicacy. Because of the risk of poisoning, the Japenese government licenses sushi chefs who wish to prepare fugu.

RS

Rajesh S.

Numerade Educator

Problem 5

Lamivudine (Epivir) is used for the treatment of HIV (AIDS) and is an example of a class of drugs called nucleoside reverse transcriptase inhibitors. These inhibitors stop HIV from infecting cells in the body. Only the $(-)$-enantiomer of lamivudine is. registored for the treatment of HIV because it is more active and less toxic than either the (t)-enantiomer or the racemate, In the $(-)$-enantiomer, the chiral centre at position 2 has the $R$ configuration and the chiral centre at position 5 has the S configuration. Draw the structure of (-)-lamivudine using hashed-wedged line notation. (Section 18.4)

RS

Rajesh S.

Numerade Educator

Problem 6

The following questions relate to (-)-menthol, a naturally occurring compound isolated from peppermint oil. (Sections $18.2$ and $18.4)$(a) Draw the preferred chair conformation of $(-)$-menthol.
(b) Assign $R$ or $S$ configuration to each of the chiral centres in (-) - menthol.

RS

Rajesh S.

Numerade Educator

Problem 7

Anatoxin-a, otherwise known as Very Fast Death Factor, is an alkaloid isolated from blue-green algae. It is a potent neurotoxin, so affects the functioning of the nervous system, often causing death due to paralysis of the respiratory muscles. The following questions relate to part of a synthesis of the ( $-$ )-enantiomer of anatoxin-a. (Sections $18.3$ and 18.4)(a) Assign the $R$ or $S$ configuration to the chiral centre in compound $1 .$
(b) Draw the enantiomer of compound 1.
(c) Does the $\mathrm{C}=\mathrm{C}$ bond in compound 2 have the $\mathrm{E}$ or $Z$ configuration?
(d) Draw the structure of compound 4 and assign the $R$ or $S$ configuration to both chiral centres.
(e) Are compounds 3 and 4 enantiomers or diastereomers?
(f) Draw the structure of $(+)$-anatoxin-a and identify the chiral centres.

RS

Rajesh S.

Numerade Educator