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12.11: Exercises

Last updated

Apr 15, 2023
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- 12.10: For Future Use
- 13: States of Matter

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LibreTexts

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12.4: Branched Alkanes

Explain why these two molecules are not isomers:

Hexane depicted as a straight chain and as a straight five carbon chain with a methyl group on the fifth carbon.

Answer: They are the same compound because each is a saturated hydrocarbon containing an unbranched chain of six carbon atoms.

Explain why these two molecules are not isomers:

Answer: The molecule on the left has a molecular formula of C₆H₁₂ while the one on the right has a molecular formula of C₆H₁₄. Since they have different numbers of hydrogens, they cannot be isomers.

Write the chemical formula and three different Lewis structures for a five-carbon alkane.

Answer: C₅H₁₂; ; ;

What are the IUPAC names of the alkanes drawn in Exercise 3?

Answer: pentane; 2-methylbutane; 2,2-dimethylpropane

In the gasoline industry, what is called isooctane is actually 2,2,4-trimethylpentane. Draw the condensed structure of isooctane.

Answer

Isooctane (see Exercise 5) is an isomer of what straight-chain alkane?

Answer: octane

Name the other three alkane isomers that contain a five-carbon chain with three methyl substituents.

Answer: 2,2,3-trimethylpentane; 2,3,4-trimethylpentane; 2,3,3-trimethylpentane

Draw the Lewis structure and line structure for each of the following hydrocarbons:
1. hexane
2. 3-methylpentane
3. heptane
4. 3-ethylhexane

Answer

;
;
;
;

Give the complete IUPAC name for each of the following compounds:
1. CH₃CH₂CH₂CH₃
4. CH₃CH₂CH₃

Answer

butane
2-methylpropane
2-methylbutane
propane
3-methylpentane

Butane is used as a fuel in disposable lighters. Write the Lewis structure for each isomer of butane.

Answer: ;

Draw line structures of and name the five structural isomers of hexane.

Answer

hexane,

2-methylpentane,

3-methylpentane,

2,3-dimethylbutane,

2,2-dimethylbutane,

12.5: Alkenes and Alkynes

Draw and name all possible normal (that is, straight-chain) isomers of heptyne.

Answer

1-heptyne,

2-heptyne,

3-heptyne,

Write the chemical formula and a Lewis structure of the following, each of which contains five carbon atoms:
1. an alkene
2. an alkyne

Answer

C₅H₁₀;
C₅H₈;

Explain why unbranched alkenes can form geometric isomers while unbranched alkanes cannot.

Answer: It is very difficult to rotate round a carbon-carbon double bond in an alkene so the location of the groups coming off of it is fixed. There is free rotation about a carbon-carbon single bond in an alkane so the groups coming off of the bond occupy all positions.

Write the chemical formula, condensed formula, and Lewis structure for each of the following hydrocarbons:
1. cis-3-hexene
2. 1-pentene
3. 3-hexyne
4. 2-pentyne
5. trans-3-heptene
6. 1-hexene
7. 2-heptyne

Answer

C₆H₁₂; ;
C₅H₁₀; ;
C₆H₁₀; ;
C₅H₈; ;
C₇H₁₄;;
C₆H₁₂;;
C₇H₁₂; ;

Give the complete IUPAC name for each of the following compounds:
2. CH₃CH₂CH₂CH=CH₂

Answer

1-butyne
1-pentene
1-octyne
trans-2-pentene
2-pentyne

Write Lewis structures for the cis–trans isomers of CH₃CH=CHCH₃.

Answer

cis:

trans:

Write Lewis structures and IUPAC names for the alkyne isomers of C₄H₆.

Answer

1-butyne:

2-butyne:

12.6: Oxygen-Containing Organic Compounds

Write the condensed structures of both isomers with the formula C₂H₆O. Label the functional group of each isomer.

Answer: CH₃CH₂OH, alcohol group; CH₃OCH₃, ether

Write the condensed structures of all isomers with the formula C₂H₆O₂. Label the functional group (or groups) of each isomer.

Answer: HOCH₂CH₂OH, two alcohol groups; CH₃OCH₂OH, ether and alcohol groups

12.7: Alcohols, Aldehydes, Carboxylic Acids, and Ketones

Draw the line structures of all the possible isomers of butanol. Include branched isomers.

Answer: , , ,

Why do the compounds hexane, hexanol, and hexene have such similar names?

Answer: They all have six carbon chains.

Write condensed formulas and provide IUPAC names for the following compounds:
1. ethyl alcohol (in beverages)
2. methyl alcohol (used as a solvent, for example, in shellac)

Answer

ethanol;

methanol;

Give the complete IUPAC name for each of the following compounds:

Answer

2-pentanone
butanal
3-hexanol
pentanoic acid

Explain why it is not possible to prepare a ketone that contains only two carbon atoms.

Answer: A ketone contains a group bonded to two additional carbon atoms; thus, a minimum of three carbon atoms are needed.

Fatty acids are carboxylic acids that have long hydrocarbon chains attached to a carboxylate group. How does a saturated fatty acid differ from an unsaturated fatty acid? How are they similar?

Answer: Since they are both carboxylic acids, they each contain the –COOH functional group and its characteristics. The difference is the hydrocarbon chain in a saturated fatty acid contains no double or triple bonds, whereas the hydrocarbon chain in an unsaturated fatty acid contains one or more multiple bonds.

Order the following molecules from least to most oxidized, based on the marked carbon atom:

Answer: Most oxidized is c; intermediate is a; least oxidized is b.

Predict the products of oxidizing the molecules shown in this problem. In each case, identify the product that will result from the minimal increase in oxidation state for the highlighted carbon atom:

Answer

Predict the products of reducing the following molecules. In each case, identify the product that will result from the minimal decrease in oxidation state for the highlighted carbon atom:

Answer

Alcohols A, B, and C all have the composition C₄H₁₀O. Molecules of alcohol A contain a branched carbon chain and can be oxidized to an aldehyde; molecules of alcohol B contain a linear carbon chain and can be oxidized to a ketone; and molecules of alcohol C can be oxidized to neither an aldehyde nor a ketone. Write the Lewis structures of these molecules.

Answer

12.8: Esters

The foul odor of rancid butter is caused by butanoic acid, CH₃CH₂CH₂CO₂H, commonly known as butyric acid.
1. Draw the Lewis structure of butyric acid.
2. The esters formed from butyric acid are pleasant-smelling compounds found in fruits and used in perfumes. Draw the Lewis structure for the ester formed from the reaction of butyric acid with 1-propanol.

Answer

Write balanced equations for each of the following reactions using condensed formulas:
1. ethanol reacts with propanoic acid
2. 1-butanol reacts with acetic acid (ethanoic acid)

Answer

12.9: Ethers

Draw the condensed structure of diethyl ether, once used as an anesthetic.

Answer: CH₃CH₂OCH₂CH₃

Draw the condensed formulas for each of the following compounds:
1. dipropyl ether
2. ethyl methyl ether

Answer

CH₃CH₂CH₂OCH₂CH₂CH₃
CH₃CH₂OCH₃

Give the common name for each of the following compounds:

Answer

butyl ethyl ether
ethyl propyl ether
methyl propyl ether

Additional Exercises

Give the IUPAC name for each of the following molecules.

Answer

4-ethyl-3-methylheptane
trans-3-hexene
2,4-dimethylhexane
3-hexanone
heptanoic acid

Write a condensed structural formula for each of the following molecules.
1. propene
2. 1-butanol
3. ethyl propyl ether
4. cis-2-heptene
5. 2,2,3-trimethylhexane
6. methanal (commonly known as formaldehyde)

Answer

CH₂=CHCH₃
CH₃CH₂CH₂CH₂OH
CH₃CH₂OCH₂CH₂CH₃

Write a condensed structural formula for each of the following molecules.
1. 2-propanol
2. acetone (2-propanone)
3. dimethyl ether
4. acetic acid (ethanoic acid)
5. 1-hexene

Answer

CH₃OCH₃
CH₂=CHCH₂CH₂CH₂CH₃

This page was adapted from "Beginning Chemistry (Ball)" by LibreTexts and "Chemistry (OpenStax)" by LibreTexts and is shared under a CC BY-NC-SA 4.0 license and was authored, remixed, and/or curated by Vicki MacMurdo (Anoka-Ramsey Community College) and Lance S. Lund (Anoka-Ramsey Community College).

12.4: Branched Alkanes

12.5: Alkenes and Alkynes

12.6: Oxygen-Containing Organic Compounds

12.7: Alcohols, Aldehydes, Carboxylic Acids, and Ketones

12.8: Esters

12.9: Ethers

Additional Exercises

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