Visualizing Chemistry

Problem 3-19

Identify the functional groups in the following substances, and convert each drawing into a molecular formula (red = O, blue = N).

(a)

(b)

Problem 3-20

Give IUPAC names for the following alkanes, and convert each drawing into a skeletal structure.

(a)

(b)

(c)

(d)

Problem 3-21

Draw a Newman projection along the C2–C3 bond of the following conformation of 2- butanol.

Functional Groups

Problem 3-22

Locate and identify the functional groups in the following molecules.

(a)

(b)

(c)

(d)

(e)

(f)

Problem 3-23

Propose structures that meet the following descriptions:

(a) A ketone with five carbons

(b) A four-carbon amide

(c) A five-carbon ester

(d) An aromatic aldehyde

(e) A keto ester

(f) An amino alcohol

Problem 3-24

Propose structures for the following:

(a) A ketone, C₄H₈O

(b) A nitrile, C₅H₉N

(c) A dialdehyde, C₄H₆O₂

(d) A bromoalkene, C₆H₁₁Br

(e) An alkane, C₆H₁₄

(f) cyclic saturated hydrocarbon, C₆H₁₂

(g) A diene (dialkene), C₅H₈

(h) A keto alkene, C₅H₈O

Problem 3-25

Predict the hybridization of the carbon atom in each of the following functional groups:

(a) Ketone (b) Nitrile (c) Carboxylic acid

Problem 3-26

Draw the structures of the following molecules:

(a) Biacetyl, C₄H₆O₂, a substance with the aroma of butter; it contains no rings or carbon–carbon multiple bonds.

(b) Ethylenimine, C₂H₅N, a substance used in the synthesis of melamine polymers; it contains no multiple bonds.

(c) Glycerol, C₃H₈O₃, a substance isolated from fat and used in cosmetics; it has an –OH group on each carbon.

Isomers

Problem 3-27

Draw structures that meet the following descriptions (there are many possibilities):

(a) Three isomers with the formula C₈H₁₈

(b) Two isomers with the formula C₄H₈O₂

Problem 3-28

Draw structures of the nine isomers of C₇H₁₆.

Problem 3-29

In each of the following sets, which structures represent the same compound and which represent different compounds?

(a)

(b)

(c)

Problem 3-30

Seven constitutional isomers have the formula C₄H₁₀O. Draw as many as you can.

Problem 3-31

Draw as many compounds as you can that fit the following descriptions:

(a) Alcohols with formula C₄H₁₀O

(b) Amines with formula C₅H₁₃N

(c) Ketones with formula C₅H₁₀O

(d) Aldehydes with formula C₅H₁₀O

(e) Esters with formula C₄H₈O₂

(f) Ethers with formula C₄H₁₀O

Problem 3-32

Draw compounds that contain the following:

(a) A primary alcohol

(b) A tertiary nitrile

(c) A secondary thiol

(d) Both primary and secondary alcohols

(e) An isopropyl group

(f) A quaternary carbon

Naming Compounds

Problem 3-33

Draw and name all monobromo derivatives of pentane, C₅H₁₁Br.

Problem 3-34

Draw and name all monochloro derivatives of 2,5-dimethylhexane, C₈H₁₇Cl.

Problem 3-35

Draw structures for the following:

(a) 2-Methylheptane

(b) 4-Ethyl-2,2-dimethylhexane

(c) 4-Ethyl-3,4-dimethyloctane

(d) 2,4,4-Trimethylheptane

(e) 3,3-Diethyl-2,5-dimethylnonane

(f) 4-Isopropyl-3-methylheptane

Problem 3-36

Draw a compound that:

(a) Has only primary and tertiary carbons

(b) Has no secondary or tertiary carbons

(c) Has no secondary or tertiary carbons

Problem 3-38

Give IUPAC names for the following compounds:

(a)

(b)

(c)

(d)

(e)

(f)

Problem 3-39

Name the five isomers of C₆H₁₄.

Problem 3-40

Explain why each of the following names is incorrect:

(a) 2,2-Dimethyl-6-ethylheptane

(b) 4-Ethyl-5,5-dimethylpentane

(c) 3-Ethyl-4,4-dimethylhexane

(d) 5,5,6-Trimethyloctane

(e) 2-Isopropyl-4-methylheptane

Problem 3-41

Propose structures and give IUPAC names for the following:

(a) A diethyldimethylhexane

(b) A (3-methylbutyl)-substituted alkane

Conformations

Problem 3-42

Consider 2-methylbutane (isopentane). Sighting along the C2–C3 bond:

(a) Draw a Newman projection of the most stable conformation.

(b) Draw a Newman projection of the least stable conformation.

(c) If a methyl-methyl eclipsing interaction “costs” 11 kJ/mol (2.5 kcal/mol) and a methyl-methyl gauche interaction “costs” 3.8 kJ/mol (0.9 kcal/mol), make a quantitative plot of energy versus rotation about the C2–C3 bond.

Problem 3-43

What are the relative energies of the three possible staggered conformations around the C2–C3 bond in 2,3-dimethylbutane? (See Problem 3-42.)

Problem 3-44

Construct a qualitative potential-energy diagram for rotation about the C–C bond of 1,2- dibromoethane. Which conformation would you expect to be most stable? Label the anti and gauche conformations of 1,2-dibromoethane.

Problem 3-45

Which conformation of 1,2-dibromoethane (Problem 3-44) would you expect to have the largest dipole moment? The observed dipole moment of 1,2-dibromoethane is μ = 1.0 D. What does this tell you about the actual conformation of the molecule?

Problem 3-46

Draw the most stable conformation of pentane, using wedges and dashes to represent bonds coming out of the paper and going behind the paper, respectively.

Problem 3-47

Draw the most stable conformation of 1,4-dichlorobutane, using wedges and dashes to represent bonds coming out of the paper and going behind the paper, respectively.

General Problems

Problem 3-48

For each of the following compounds, draw an isomer that has the same functional groups.

(a)

(b)

(c)

(d)

(e)

(f)

Problem 3-49

Malic acid, C₄H₆O₅, has been isolated from apples. Because this compound reacts with 2 molar equivalents of base, it is a dicarboxylic acid.

(a) Draw at least five possible structures.

(b) If malic acid is a secondary alcohol, what is its structure?

Problem 3-50

Formaldehyde, H₂C=O, is known to all biologists because of its usefulness as a tissue preservative. When pure, formaldehyde trimerizes to give trioxane, C₃H₆O₃, which, surprisingly enough, has no carbonyl groups. Only one monobromo derivative (C₃H₅BrO₃) of trioxane is possible. Propose a structure for trioxane.

Problem 3-51

The barrier to rotation about the C–C bond in bromoethane is 15 kJ/mol (3.6 kcal/mol).

(a) What energy value can you assign to a hydrogen-bromine eclipsing interaction?

(b) Construct a quantitative diagram of potential energy versus bond rotation for bromoethane.

Problem 3-52

Increased substitution around a bond leads to increased strain. Take the four substituted butanes listed below, for example. For each compound, sight along the C2–C3 bond and draw Newman projections of the most stable and least stable conformations. Use the data in Table 3.5 to assign strain-energy values to each conformation. Which of the eight conformations is most strained? Which is least strained?

(a) 2-Methylbutane

(b) 2,2-Dimethylbutane

(c) 2,3-Dimethylbutane

(d) 2,2,3-Trimethylbutane

Problem 3-53

The cholesterol-lowering agents called statins, such as simvastatin (Zocor) and pravastatin (Pravachol), are among the most widely prescribed drugs in the world, with annual sales estimated at approximately $25 billion. Identify the functional groups in both, and tell how the two substances differ.

Problem 3-54

In the next chapter we’ll look at cycloalkanes—saturated cyclic hydrocarbons—and we’ll see that the molecules generally adopt puckered, nonplanar conformations. Cyclohexane, for instance, has a puckered shape like a lounge chair rather than a flat shape. Why?

Problem 3-55

We’ll see in the next chapter that there are two isomeric substances, both named 1,2- dimethylcyclohexane. Explain.