Organic Chemistry : Help with Alkane Reactions

Study concepts, example questions & explanations for Organic Chemistry

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Example Questions

Example Question #2 : Functional Group Reactions

Which of the following can reduce an alkene to an alkane?

Possible Answers:

H2/Pd

H2/Raney nickel

Lithium aluminum hydride (LiAlH4)

Lithium aluminum hydride (LiAlH4) and H2/Pd

H2/Pd and H2/Raney nickel

Correct answer:

H2/Pd and H2/Raney nickel

Explanation:

Neither lithium aluminum hydride, nor sodium borohydride will reduce C–C double bonds.

H2/Raney nickel and H2/Pd can each (individually) reduce an alkene to an alkane. Since both H2/Raney nickel and H2/Pd can reduce the alkene, the answer is both of those reagents. This is a catalytic hydrogenation reaction, and H2/Raney nickel not only reduces C–C double bonds, but also carbonyl compounds.

Example Question #3 : Functional Group Reactions

Identify the major organic product expected from the acid-catalyzed dehydration of 2-methyl-2-pentanol.

Possible Answers:

3-methyl-1-pentene

2-methyl-2-pentene

2-methyl-1-pentene

None of the other answers

cis-3-methyl-2-pentene

Correct answer:

2-methyl-2-pentene

Explanation:

The initial compound is a five-carbon alkane chain with methyl and hydroxy groups on the second carbon. Dehydration involves the hydrogenation of the hydroxy group. That group then leaves, and a double bond is formed. Zaitsev's rule states that double bonds are more stable on more highly substituted carbons. The double bond forms across carbons two and three.

Example Question #1 : Help With Alkane Reactions

If an alkane is reacted with excess  in a high temperature environment, what are the products formed?

Possible Answers:

 and 

 and 

 and 

 and 

Correct answer:

 and 

Explanation:

Whenever an alkane is reacted with excess oxygen in a high temperature reaction, the reaction is known as combustion. Combustion of an alkane always produces carbon dioxide gas and water vapor.

Therefore the correct answer is:  and .

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