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

Alkanes, Cycloalkanes, and Alkenes: Isomers, Conformations, and Stabilities
End of Chapter Problems

1. 4.15 Give a dashed-wedged representation for the following molecules.

1. 2-Butanol (dashed-wedged representation about C₂)

2. Cyclopentanol (dashed-wedged representation about C₁)

3. 4-Bromo-2-pentanol (dashed-wedged representations about C₂ and C₄)

2. 4.16 Answer the following questions that relate to 1,2-dibromoethane.

1. Give the Newman projection and dashed/wedge representation of the least stable conformer of 1,2-dibromoethane.

2. Consider the most stable conformer of 1,2-dibromoethane, give the Newman projection of the conformer that results after rotation about the carbon—carbon bond by 60°.

3. Consider the most stable conformer of 1,2-dibromoethane, give the dashed-wedge representation of the conformer that results after rotation about the carbon—carbon bond by 180° has occurred.

4. Using the Newman projection, draw all possible staggered conformations of 1,2-dibromoethane.

5. Using the dashed-wedged representation, draw all possible eclipsed conformations of 1,2-dibromoethane.

3. 4.17 Consider carefully the conformers of molecules A and B shown.

Assume that the trend in size for the groups of molecules A and B is:

I > C₂H₅> CH₃> H, i.e. the largest is the iodine atom.

1. Draw the Newman projection for the most stable conformer of molecule A.

2. Draw the dashed-wedge representation of the least stable conformer of molecule B.

3. Draw the Newman projection that results after rotation about the middle C─C bond of molecule A by 180°.

4. 4.18

1. Draw a chair conformation of the molecule shown below.

2. Now convert your structure to the other chair conformer.

3. Which of the two conformers that you have drawn above is the most stable? Explain your answer.

5. 4.19 Answer the following questions that relate to dimethylcyclohexane.

1. Draw the chair conformer of the least stable conformer of 1,4-dimethylcyclohexane

2. Draw the chair conformer of the most stable conformer of 1,4-dimethylcyclohexane

3. Draw the chair conformer of the least stable conformer of 1,2-dimethylcyclohexane

4. Draw a trans conformer of 1,4-dimethylcyclohexane

5. Draw a cis conformer of 1,3-dimethylcyclohexane

6. 4.20 Give complete IUPAC names, including E or Z assignment, for the following molecules.