Organic Chemistry: Concepts and Applications - Headley Allan D. 2020

Stereochemistry
End of Chapter Problems

1. 5.9 Arrange the following groups in decreasing order of priorities (highest first).

2. 5.10 Using (E)-(Z) designation, give the IUPAC names for the following compounds.

3. 5.11 Give the complete name (including E, Z prefix) of the following molecule.

4. 5.12 The structures of two naturally occurring amino acids, L-alanine and L-phenylalanine, are shown below. What is the absolute configuration of the stereogenic center in each?

5. 5.13 What is the relationship between the following compounds, i.e. same, different, enantiomers, diastereomers, etc.?

6. 5.14 Define the following: (a) stereogenic center; (b) enantiomers; (c) racemic mixture; (d) diastereomers; (e) meso compound.

7. 5.15 Label each of the following compounds as optical active or optical inactive; explain each answer.

1. cis-1,3-Dimethylcyclohexane

2. trans-1,3-Dimethylcyclohexane

3. cis-1-Chloro-3-methylcyclohexane

4. trans-1-Chloro-3-methylcyclohexane

5. cis,cis-1,3,5-Trimethylcyclohexane

6. trans,trans-1,3,5-Trimethylcyclohexane

7. cis,cis-1-Chloro-3,5-dimethylcyclohexane

8. trans,cis-1-Chloro-3,5-dimethylcyclohexane

8. 5.16 Draw dashed/wedge three-dimensional structures of two different stereoisomers of each of the following compounds and determine the absolute configuration (R or S) around each chiral carbon.

9. 5.17

i. Draw a Fischer projection for (1S,2R)-1,2-dibromo-1,2-dichloroethane. Is this compound optically active? Explain your answer.

ii. Draw a Fischer projection for (1S,2S)-1,2-dibromo-1,2-dichloroethane. Is this compound optically active or optically inactive? Explain your answer.

10. 5.18 Draw the structure of the most stable conformer of the following molecules:

0. trans-1,3-Dichlorocyclohexane

1. cis-2-Chlorocyclohexanol (assume that ─Cl is larger than ─OH)

11. 5.19

0. How many stereogenic centers are found in vitamin E structure shown below?

1. Use dashed-wedge representation to assign each of the chiral carbons identified with the S configuration.

12. 5.20 Shown below is the structure of α-terpineol, with its stereogenic center starred. What is the configuration, (R) or (S), at the starred C atom?

13. 5.21 Consider carefully the following molecules (A, B, and C) shown below:

. Give complete IUPAC names (including stereochemistry) for the molecules A, B, and C.

i. What is the relationship between the following pairs of molecules: A and B; A and C; B and C, i.e. same, enantiomers, diastereomers, etc.?

14. 5.22 Identify the chiral carbons in the molecules shown below.

15. 5.23 What is the absolute configuration, (R) or (S), at the starred C atoms for the molecules below?

16. 5.24 Analyze carefully the structures shown below, I through VI, and answer the following questions. Possible choices include enantiomers, structural isomers, same molecules, diastereomers, or meso compounds.

0. What is the relationship between molecule (V) and molecule (VI)?

1. What is the relationship between molecule (I) and molecule (II)?

2. What is the relationship between molecule (II) and molecule (III)?

3. What is the relationship between molecule (IV) and molecule (VI)?

4. What is the relationship between molecule (IV) and molecule (V)?

5. What is the relationship between molecule (I) and molecule (III)?

17. 5.25 Shown below is the structure of ethambutol, which is used to treat tuberculosis. There are two chiral centers in this molecule. The S,S isomer is the active form, whereas the R,R causes optical neuritis, and eventually results in blindness.

0. For the molecule above, clearly circle the two chiral (stereogenic) centers.

1. Draw the S,S enantiomer of ethambutol and clearly show the stereochemistry around each chiral carbon by using dashed-wedge representation.

18. 5.26 Shown below is the structure of taxol, a drug that is used to cure cervical cancer. It has many stereogenic centers; identify the stereogenic centers in this molecule.