Alkanes

Question: The eclipsed conformation of $\mathit{C}{\mathit{H}}_{\mathbf{3}}\mathit{C}{\mathit{H}}_{\mathbf{2}}\mathit{C}\mathit{l}$  is   $\mathbf{15}\mathbf{ }\mathit{k}\mathit{J}\mathbf{/}\mathit{m}\mathit{o}\mathit{l}$ less stable than the staggered conformation. How much is the H, Cl eclipsing interaction worth in destabilization?

Question: a. Draw the anti and gauche conformations for ethylene glycol $\left(OHC{H}_{2}C{H}_{2}OH\right)$ .

b. Ethylene glycol is unusual in that the gauche conformation is more stable than the anti conformation. Offer an explanation. 

Question: For each compound drawn below: 

a. Label each OH, Br, and$\mathit{C}{\mathit{H}}_{\mathbf{3}}$group as axial or equatorial.

b. Classify each conformation as cis or trans. 

c. Translate each structure into a representation with a hexagon for the six-membered ring, and wedges and dashed wedges for groups above and below the ring. 

d. Draw the second possible chair conformation for each compound. 

Question: Draw the two possible chair conformations for cis-1,3-dimethylcyclohexane. Which conformation, if either, is more stable?

Question: For each compound drawn below: 

a. Draw representations for the cis and trans isomers using a hexagon for the six membered ring, and wedges and dashed wedges for substituents. 

b. Draw the two possible chair conformations for the cis isomer. Which conformation, if either, is more stable? 

c. Draw the two possible chair conformations for the trans isomer. Which conformation, if either, is more stable? 

d. Which isomer, cis or trans, is more stable and why?

Question: Convert each of the following structures into its more stable chair form. One structure represents menthol and one represents isomenthol. Menthol, the more stable isomer, is used in lip balms and mouthwash. Which structure corresponds to menthol?

Question: Answer the following questions about compound A, which contains a $\mathbf{-}\mathit{C}{\mathit{H}}_{\mathbf{3}}$ group and OH group bonded to the carbon skeleton that consists of three six-membered rings in the conformation shown.

a. Are the $\mathbf{-}\mathit{C}{\mathit{H}}_{\mathbf{3}}$ and OH groups oriented cis or trans to each other?

b. Is a substituent on ${\mathit{C}}_{\mathbf{a}}$ that is cis to the $\mathit{C}{\mathit{H}}_{\mathbf{3}}$  group located in the axial or equatorial position?

c. Is an equatorial Br at ${\mathit{C}}_{\mathbf{b}}$ oriented cis or trans to the OH group?

d. Is the H atom on ${\mathit{C}}_{\mathbf{c}}$ located cis or trans to the OH group?

e. Is a substituent on ${\mathit{C}}_{\mathbf{d}}$ that is trans to the OH group located in the axial or equatorial position?

Question: Glucose is a simple sugar with five substituents bonded to a six-membered ring.

a. Using a chair representation, draw the most stable arrangement of these substituents on the six-membered ring.

b. Convert this representation into one that uses a hexagon with wedges and dashed wedges.

c. Draw a constitutional isomer of glucose. 

d. Draw a stereoisomer that has an axial OH group on one carbon.

Question: Classify each pair of compounds as constitutional isomers, stereoisomers, identical molecules, or not isomers of each other.

a. 

b.

c.

d.

Question: Classify each pair of compounds as constitutional isomers or identical molecules.

a. 

b.

Question: Answer the following questions about compounds A–D.

a. How are the compounds in each pair related? Choose from constitutional isomers, stereoisomers, or identical molecules: A and B; A and C; B and D.

b. Label each compound as a cis or trans isomer.

c. Draw B as a hexagon with wedges and dashed wedges to show the stereochemistry of substituents.

d. Draw a stereoisomer of A as a hexagon using wedges and dashed wedges to show the orientation of substituents.

Question: Draw the three constitutional isomers having molecular formula ${\mathit{C}}_{\mathbf{7}}{\mathit{H}}_{\mathbf{14}}$ that contain a five-membered ring and two methyl groups as substituents. For each constitutional isomer that can have cis and trans isomers, draw the two stereoisomers.

Question: Classify each reaction as oxidation, reduction, or neither.

a. 

b.

Question: Draw the products of combustion of each alkane.

a.

b.

Question: Hydrocarbons like benzene are metabolized in the body to arene oxides, which rearrange to form phenols. This is an example of a general process in the body, in which an unwanted compound (benzene) is converted to a more water-soluble derivative called a metabolite, so that it can be excreted more readily from the body.

a. Classify each of these reactions as oxidation, reduction, or neither.

b. Explain why phenol is more water soluble than benzene. This means that phenol dissolves in urine, which is largely water, to a greater extent than benzene.

Question: Cholic acid, a compound called a bile acid, is converted to a bile salt in the body. Bile salts have properties similar to soaps, and they help transport lipids through aqueous solutions. Explain why this is so.

Question: Mineral oil, a mixture of high molecular weight alkanes, is sometimes used as a laxative. Why are individuals who use mineral oil for this purpose advised to avoid taking it at the same time they consume foods rich in fat-soluble vitamins such as vitamin A?

Question: Cyclopropane and cyclobutane have similar strain energy despite the fact that the C-C-C bond angles of cyclopropane are much smaller than those of cyclobutane. Suggest an explanation for this observation, considering all sources of strain discussed in Chapter 4.

Question: Although penicillin G has two amide functional groups, one is much more reactive than the other. Which amide is more reactive and why?

Question: Haloethanes $\left(C{H}_{3}C{H}_{2}X, X=Cl, Br, I\right)$ have similar barriers to rotation (13.4–15.5 kJ/mol) despite the fact that the size of the halogen increases, $\mathit{C}\mathit{l}\mathbf{\to }\mathit{B}\mathit{r}\mathbf{\to }\mathit{I}$ . Offer an explanation.

Question: When two six-membered rings share a C-C bond, this bicyclic system is called decalin. There are two possible arrangements: trans-decalin having two hydrogen atoms at the ring fusion on opposite sides of the rings, and cis-decalin having the two hydrogens at the ring fusion on the same side.

1. Draw trans- and cis-decalin using the chair form for the cyclohexane rings.
2. The trans isomer is more stable. Explain why.

Question: Consider the tricyclic structure A. 

(a) Label each substituent on the rings as axial or equatorial. 

(b) Draw a skeletal structure for A, using wedges and dashed wedges to show whether the substituents are located above or below the rings.

                                   A

Question: Consider the tricyclic structure B. 

(a) Label each substituent on the rings as axial or equatorial.

(b) Draw B using chair conformations for each six-membered ring. 

(c) Label the atoms on the ring fusions (the carbons that join each set of two rings together) as cis or trans to each other.

                           B

Question: Read Appendix B on naming branched alkyl substituents, and draw all possible alkyl groups having the formula ${\mathit{C}}_{\mathbf{5}}{{\mathit{H}}_{\mathbf{11}}}^{\mathbf{-}}$ . Give the IUPAC names for the eight compounds of molecular formula  ${\mathit{C}}_{\mathbf{10}}{\mathit{H}}_{\mathbf{20}}$ that contain a cyclopentane ring with each of these alkyl groups as a substituent.

Question: Read Appendix B on naming bicyclic compounds. Then give the IUPAC name for each of the following compounds.

a.

b.

c.

d.

Give the IUPAC name for each compound.

a

b. 

c. 

d. 

e. 

f. 

Give the structure corresponding to each IUPAC name. 

a. 1,2-dimethylcyclobutane     

b. 1,1,2-trimethylcyclopropane 

c. 4-ethyl-1,2-dimethylcyclohexane

d. 1-sec-butyl-3-isopropylcyclopentane

e. 1,1,2,3,4-pentamethylcycloheptane

Arrange the following compounds in order of increasing boiling point.

Draw the staggered and eclipsed conformations that result from rotation around the C-C bond in ${\mathrm{CH}}_3-{\mathrm{CH}}_2\mathrm{Br}$.

Which of the following is (are) possible Newman projections for 2-methylpentane?