Alkanes

Question: Three components of the sex pheromone of the female sand bee (Ophrys sphegodes) are saturated hydrocarbons containing 23, 25, and 27 carbon atoms. How many H atoms does each of these alkanes contain? Interestingly, the early spider orchid emits a similar hydrocarbon mixture to attract male sand bees to pollinate its flowers.

Question: Which of the following is not another representation for 2-methylbutane?

a. 

b.

c.

d.

Question: Draw the five constitutional isomers having molecular formula  ${\mathit{C}}_{\mathbf{6}}{\mathit{H}}_{\mathbf{14}}$.

Question: Review classifying carbons and hydrogens in Section 3.2, and draw the structure of an alkane with molecular formula ${\mathit{C}}_{\mathbf{7}}{\mathit{H}}_{\mathbf{16}}$  that contains

a. one ${\mathbf{4}}^{\mathbf{0}}$ carbon; 

b. only  ${\mathbf{1}}^{\mathbf{0}}$ and ${\mathbf{2}}^{\mathbf{0}}$  carbons; 

c. ${\mathbf{1}}^{\mathbf{0}}$ , ${\mathbf{2}}^{\mathbf{0}}$ , and ${\mathbf{3}}^{\mathbf{0}}$  hydrogens.

Question: a. Which compounds (B–F) are identical to A? b. Which compounds (B–F) represent an isomer of A?

Question: Draw the five constitutional isomers that have molecular formula ${\mathit{C}}_{\mathbf{5}}{\mathit{H}}_{\mathbf{10}}$ and contain one ring.

Question: Give IUPAC name of each compound.

a. 

b.

c.

d.

Question: Give IUPAC name of each compound.

a. ${\left(C{H}_3\right)}_{\mathbf{3}}\mathbf{-}\mathit{C}{\mathit{H}}_{\mathbf{2}}\mathbf{-}\mathit{C}\mathit{H}\mathbf{-}{\left(C{H}_{2}C{H}_3\right)}_{\mathbf{2}}$

b. 

c.$\mathit{C}{\mathit{H}}_{\mathbf{3}}{\left(C{H}_2\right)}_{\mathbf{3}}\mathit{C}\mathit{H}\left(C{H}_{2}C{H}_{2}C{H}_3\right)\mathit{C}\mathit{H}{\left(C{H}_3\right)}_{\mathbf{2}}$

d. 

Question: Give the structure corresponding to each IUPAC name.

1. 3-methylhexane
2. 3,3-dimethylpentane
3. 3,5,5-trimethyloctane
4. 3-ethyl-4-methylhexane
5. 3-ethyl-5-isobutylnonane

Question: Give the IUPAC name for each of the five constitutional isomers of molecular formula ${\mathit{C}}_{\mathbf{6}}{\mathit{H}}_{\mathbf{14}}$  in Problem 4.3.

Question: Give the IUPAC name for each compound.

Question: Give the structure corresponding to each IUPAC name. 

a. 1,2-dimethylcyclobutane d. 1-sec-butyl-3-isopropylcyclopentane 

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

c. 4-ethyl-1,2-dimethylcyclohexane

Question: Arrange the following compounds in order of increasing boiling point.

Question: Draw the staggered and eclipsed conformations that result from rotation around the C-C bond in $\mathit{C}{\mathit{H}}_{\mathbf{3}}\mathbf{-}\mathit{C}{\mathit{H}}_{\mathbf{2}}\mathit{B}\mathit{r}$ .

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

Question: The torsional energy in propane is 14 kJ/mol (3.4 kcal/mol). Because each H,H eclipsing interaction is worth 4.0 kJ/mol (1.0 kcal/mol) of destabilization, how much is one H, $\mathit{C}{\mathit{H}}_{\mathbf{3}}$  eclipsing interaction worth in destabilization? (See Section 4.10 for an alternate way to arrive at this value.)

Question: a.Draw the three staggered and three eclipsed conformations that result from rotation around the bond labeled in red using Newman projections. b. Label the most stable and least stable conformation.

Question: Rank the following conformations in order of increasing energy.

Question: Consider rotation around the carbon-carbon bond in 1,2-dichloroethane $\left(ClC{H}_{2}C{H}_{2}Cl\right)$.

a. Using Newman projections, draw all of the staggered and eclipsed conformations that result from rotation around this bond. 

b. Graph energy versus dihedral angle for rotation around this bond.

Question: Calculate the destabilization present in each eclipsed conformation.

a. 

b.

Question: Classify the ring carbons as up C’s or down C’s. Identify the bonds highlighted in bold as axial or equatorial.

Question: Using the cyclohexane with the C’s numbered as shown, draw a chair form that fits each description.

a. The ring has an axial $\mathit{C}{\mathit{H}}_{\mathbf{3}}$ group at C1 and an equatorial OH on C2.

b. The ring has an equatorial $\mathit{C}{\mathit{H}}_{\mathbf{3}}$ group on C6 and an axial OH group on C4.

c. The ring has equatorial OH groups on C1, C2, and C5.

Question: Draw a second chair conformation for each cyclohexane. Then decide which conformation is present in higher concentration at equilibrium.

a. 

b.

c.

Question: Draw both conformations for 1-ethyl-1-methylcyclohexane and decide which conformation (if any) is more stable.

Question: Draw the structure for each compound using wedges and dashed wedges.

1. cis-1,2-dimethylcyclopropane                
2. trans-1-ethyl-2-methylcyclopentane

Question: For cis-1,3-diethylcyclobutane, draw (a) a stereoisomer; (b) a constitutional isomer.

Question: Label each compound as cis or trans. Then draw the second chair conformation.

a.

b.

c.

Question: Consider 1,2-dimethylcyclohexane.

1. Draw structures for the cis and trans isomers using a hexagon for the six-membered ring.
2. Draw the two possible chair conformations for the cis isomer. Which conformation, if either, is more stable?
3. Draw the two possible chair conformations for the trans isomer. Which conformation, if either, is more stable?
4. Which isomer, cis or trans, is more stable and why?

Question: Draw a chair conformation of cyclohexane with one $\mathit{C}{\mathit{H}}_{\mathbf{3}}\mathit{C}{\mathit{H}}_{\mathbf{2}}$  group and one $\mathit{C}{\mathit{H}}_{\mathbf{3}}$  group that fits each description.

1. a 1,1-disubstituted cyclohexane with an axial $\mathit{C}{\mathit{H}}_{\mathbf{3}}\mathit{C}{\mathit{H}}_{\mathbf{2}}$ group
2. a cis-1,2-disubstituted cyclohexane with an axial $\mathit{C}{\mathit{H}}_{\mathbf{3}}$ group
3. a trans-1,3-disubstituted cyclohexane with an equatorial $\mathit{C}{\mathit{H}}_{\mathbf{3}}$ group
4. a trans-1,4-disubstituted cyclohexane with an equatorial $\mathit{C}{\mathit{H}}_{\mathbf{3}}\mathit{C}{\mathit{H}}_{\mathbf{2}}$ group 

Question: Classify each transformation as an oxidation, reduction, or neither.

a.

b.

c.

d.

Question: Draw the products of each combustion reaction.

a.

b.

Question: Explain why beeswax is insoluble in ${\mathit{H}}_{\mathbf{2}}\mathit{O}$ , slightly soluble in ethanol $\left(C{H}_{3}C{H}_{2}OH\right)$ , and soluble in chloroform $\left(CHC{l}_3\right)$ .

Question: Pristane is a high molecular weight alkane present in shark liver oil, a lipid used as a folk remedy and lubricant by coastal societies in northern Europe for centuries. What is the IUPAC name for pristane?

Pristane

Question: Name each alkane using the ball-and-stick model, and classify each carbon as  ${\mathbf{1}}^{\mathbf{0}}\mathbf{,}{\mathbf{2}}^{\mathbf{0}}\mathbf{,}{\mathbf{3}}^{\mathbf{0}}$, or ${\mathbf{4}}^{\mathbf{0}}$ .

a. 

b.

Question: Consider the substituted cyclohexane shown in the ball-and-stick model.

1. Label the substituents on C1, C2, and C4 as axial or equatorial.
2. Are the substituents on C1 and C2 cis or trans to each other?
3. Are the substituents on C2 and C4 cis or trans to each other?
4. Draw the second possible conformation in the chair form, and classify it as more stable or less stable than the conformation shown in the three-dimensional model.

Question: Convert each three-dimensional model to a Newman projection around the indicated bond.

Question: Draw the structure of all compounds that fit the following descriptions. a. Five constitutional isomers having the molecular formula ${\mathit{C}}_{\mathbf{4}}{\mathit{H}}_{\mathbf{8}}$ b. Nine constitutional isomers having the molecular formula ${\mathit{C}}_{\mathbf{7}}{\mathit{H}}_{\mathbf{16}}$ c. Twelve constitutional isomers having the molecular formula ${\mathit{C}}_{\mathbf{6}}{\mathit{H}}_{\mathbf{12}}$  and containing one ring

Question: Give the IUPAC name for each compound.

                            j

Question: Give the structure and IUPAC name for each of the nine isomers having molecular formula ${\mathit{C}}_{\mathbf{9}}{\mathit{H}}_{\mathbf{20}}$ that contains seven carbons in the longest chain and two methyl groups as substituents.

Question: Draw the structure corresponding to each IUPAC name. 

a. 3-ethyl-2-methylhexane  

b. sec-butylcyclopentane 

c. 4-isopropyl-2,4,5-trimethylundecane 

d. cyclobutylcycloheptane 

e. 3-ethyl-1,1-dimethylcyclohexane 

f. 4-butyl-1,1-diethylcyclooctane

g. 6-isopropyl-2,3-dimethyldodecane

h. 2,2,6,6,7-pentamethyloctane

i. cis-1-ethyl-3-methylcyclopentane

j. trans-1-tert-butyl-4-ethylcyclohexane

Question: Each of the following IUPAC names is incorrect. Explain why it is incorrect and give the correct IUPAC name. 

a. 2,2-dimethyl-4-ethylheptane 

b. 5-ethyl-2-methylhexane 

c. 2-methyl-2-isopropylheptane 

d. 1,5-dimethylcyclohexane 

e. 1-ethyl-2,6-dimethylcycloheptane

f. 5,5,6-trimethyloctane

g. 3-butyl-2,2-dimethylhexaneh. 1,3-dimethylbutane

Question: Give the IUPAC name for each compound.

Question: Rank the following alkanes in order of increasing boiling point.

Question: The melting points and boiling points of two isomeric alkanes are as follows: $\mathit{C}{\mathit{H}}_{\mathbf{3}}{\left(C{H}_2\right)}_{\mathbf{6}}\mathit{C}{\mathit{H}}_{\mathbf{3}}$ , $\mathit{m}\mathit{p}\mathbf{ }\mathbf{=}\mathbf{-}{\mathbf{57}}^{\mathbf{0}}\mathit{C}$  and $\mathit{b}\mathit{p}\mathbf{=}{\mathbf{126}}^{\mathbf{0}}\mathit{C}$ ;${\left(C{H}_3\right)}_{\mathbf{3}}\mathit{C}\mathit{C}{\left(C{H}_3\right)}_{\mathbf{3}}$  , $\mathit{m}\mathit{p}\mathbf{=}{\mathbf{102}}^{\mathbf{0}}\mathit{C}$  and $\mathit{b}\mathit{p}\mathbf{=}{\mathbf{106}}^{\mathbf{0}}\mathit{C}$ .

a. Explain why one isomer has a lower melting point but higher boiling point. 

b. Explain why there is a small difference in the boiling points of the two compounds but a huge difference in their melting points. 

Question: Which conformation in each pair is higher in energy? Calculate the energy difference between the two conformations using the values given in Table 4.3.

a.

b.

Question: Considering rotation around the bond highlighted in pink in each compound, draw Newman projections for the most stable and least stable conformations.

a. 

b.

Question: Convert each structure to a Newman projection around the bond highlighted in pink.

a.

b.

c.

Question: a. Using Newman projections, draw all staggered and eclipsed conformations that result from rotation around the bond highlighted in pink in each molecule; 

b. draw a graph of energy versus dihedral angle for rotation around this bond.

Question: Label the sites of torsional and steric strain in each conformation.

a.

b.

c.

Question: Calculate the barrier to rotation for each bond highlighted in pink.

a.

b.