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12.11: Exercises

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    12.4:  Branched Alkanes

    1. 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.

     

    1. Explain why these two molecules are not isomers:

      CH3CH2CH2CHCHCH3 and CH3CH2CH2CH(CH3)2

    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.

     

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

    C5H12;  ;  ; 

     

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

    pentane; 2-methylbutane; 2,2-dimethylpropane

     

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

     

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

    octane

     

    1. 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

     

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

     

    1. Give the complete IUPAC name for each of the following compounds:
      1. CH3CH2CH2CH3
      4. CH3CH2CH3
    Answer
    1. butane
    2. 2-methylpropane
    3. 2-methylbutane
    4. propane
    5. 3-methylpentane

     

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

    ; 

     

    1. 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

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

    1-heptyne,   

    2-heptyne,   

    3-heptyne, 

     

    1. 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
    1. C5H10; 
    2. C5H8; 

     

    1. 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.

     

    1. 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
    1. C6H12;  ; 
    2. C5H10;  ; 
    3. C6H10;  ; 
    4. C5H8;  ; 
    5. C7H14; ; 
    6. C6H12; ; 
    7. C7H12;  ; 

     

    1. Give the complete IUPAC name for each of the following compounds:
      2. CH3CH2CH2CH=CH2
    Answer
    1. 1-butyne
    2. 1-pentene
    3. 1-octyne
    4. trans-2-pentene
    5. 2-pentyne

     

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

    cis:  

    trans:  

     

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

    1-butyne:  

    2-butyne:  

     

    12.6:  Oxygen-Containing Organic Compounds

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

    CH3CH2OH, alcohol group; CH3OCH3, ether

     

    1. 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

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

    ,  ,  , 

     

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

    They all have six carbon chains.

     

    1. 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; 

     

    1. Give the complete IUPAC name for each of the following compounds:
    Answer
    1. 2-pentanone
    2. butanal
    3. 3-hexanol
    4. pentanoic acid

     

    1. 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.

     

    1. 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.

     

    1. 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.

     

    1. 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

     

    1. 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

     

    1. 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

    1. 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

     

    1. 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

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

    CH3CH2OCH2CH3

     

    1. Draw the condensed formulas for each of the following compounds:
      1. dipropyl ether
      2. ethyl methyl ether
    Answer
    1. CH3CH2CH2OCH2CH2CH3
    2. CH3CH2OCH3

     

    1. Give the common name for each of the following compounds:
    Answer
    1. butyl ethyl ether
    2. ethyl propyl ether
    3. methyl propyl ether

     

    Additional Exercises

    1. Give the IUPAC name for each of the following molecules.
    Answer
    1. 4-ethyl-3-methylheptane
    2. trans-3-hexene
    3. 2,4-dimethylhexane
    4. 3-hexanone
    5. heptanoic acid

     

    1. 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
    1. CH2=CHCH3
    2. CH3CH2CH2CH2OH
    3. CH3CH2OCH2CH2CH3
    4. cis-2-heptene condensed structure.JPG

     

    1. 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
    3. CH3OCH3
    5. 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).

    This page titled 12.11: Exercises is shared under a CC BY-NC-SA 4.0 license and was authored, remixed, and/or curated by Anonymous.