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Chapter 3: Problem 5

Write the six isomers of \(\mathrm{C}_{5} \mathrm{H}_{10}\) that are alkenes (the pentenes). There are 17 isomers of \(\mathrm{C}_{6} \mathrm{H}_{12}\) that are alkenes (the hexenes). Draw six of them. Be alert for isomerism of the cis/trans [or \((Z / E)]\) kind in these molecules.

Short Answer

Expert verified
Six isomers of \(\text{C}_5 \text{H}_{10}\) are: 1-pentene, cis-2-pentene, trans-2-pentene, 2-methyl-1-butene, 2-methyl-2-butene, and 3-methyl-1-butene. Examples of six isomers of \(\text{C}_6 \text{H}_{12}\) are: 1-hexene, cis-2-hexene, trans-2-hexene, 3-hexene, 2-methyl-1-pentene, and 3-methyl-1-pentene.

Step by step solution

01

Understand the Isomers of \(\text{C}_5 \text{H}_{10}\)

Isomers are compounds that have the same molecular formula but different structural formulas. Begin by noting that \(\text{C}_5 \text{H}_{10}\) must have a double bond to satisfy the criteria for alkenes.
02

Draw the Linear Pentenes

Draw the straight-chain isomers first. These include: 1-pentene and 2-pentene. Remember that 2-pentene can exhibit cis/trans isomerism: cis-2-pentene and trans-2-pentene.
03

Draw the Branched Pentenes

Draw the branched-chain isomers. These include: 2-methyl-1-butene, 2-methyl-2-butene, and 3-methyl-1-butene.
04

List All Isomers of \(\text{C}_5 \text{H}_{10}\)

Summarize the six isomers of \(\text{C}_5 \text{H}_{10}\): 1-pentene, cis-2-pentene, trans-2-pentene, 2-methyl-1-butene, 2-methyl-2-butene, and 3-methyl-1-butene.
05

Understand the Isomers of \(\text{C}_6 \text{H}_{12}\)

For \(\text{C}_6 \text{H}_{12}\), there are 17 different structural isomers. Each must have a double bond to fulfill the criteria for alkenes.
06

Draw Six Hexene Isomers

Illustrate six distinct isomers of \(\text{C}_6 \text{H}_{12}\). Examples are 1-hexene, cis-2-hexene, trans-2-hexene, 3-hexene, 2-methyl-1-pentene, and 3-methyl-1-pentene.

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Key Concepts

These are the key concepts you need to understand to accurately answer the question.

structural isomerism
Structural isomerism is a type of isomerism where compounds have the same molecular formula but different structural formulas. This means the atoms are arranged differently in each isomer. For example, \(\text{C}_5 \text{H}_{10}\), an alkene, has six isomers: 1-pentene, cis-2-pentene, trans-2-pentene, 2-methyl-1-butene, 2-methyl-2-butene, and 3-methyl-1-butene. The way the carbon atoms are connected varies among these isomers, resulting in different compounds.
cis/trans isomerism
Cis/trans isomerism, also known as \(Z/E\) isomerism, occurs in alkenes due to restricted rotation around the double bond. If the two identical or similar groups are on the same side of the double bond, it is a cis isomer. If they are on opposite sides, it’s a trans isomer. For example, in 2-pentene, we have two cis/trans isomers: cis-2-pentene (both substituents on the same side), and trans-2-pentene (substituents across from each other). Recognizing the difference is crucial for understanding the physical and chemical properties of alkenes.
alkene nomenclature
Naming alkenes follows the IUPAC system. Here’s a simple guide:
  • Identify the longest carbon chain containing the double bond.
  • Number the chain so the double bond has the lowest possible number.
  • Name and position substituents as prefixes.
For example, in \(2-methyl-2-butene\), the longest chain with a double bond has four carbons (butene), and the double bond starts at carbon 2. There’s a methyl group on the second carbon, hence the name.
organic chemistry
Organic chemistry deals with compounds made primarily of carbon and hydrogen. Alkenes are one type of hydrocarbon characterized by at least one carbon-carbon double bond. Understanding organic chemistry concepts like isomerism and nomenclature is essential for identifying and drawing isomers. This field studies the reactions, structures, and properties of organic molecules, which are the building blocks of life.
molecular formula interpretation
Interpreting molecular formulas is key in chemistry. Take \(C_5H_{10}\) and \(C_6H_{12}\). Both indicate alkenes with double bonds due to the general formula \(C_nH_{2n}\). The formula alone doesn’t specify structure, leading to multiple isomers. From \(\text{C}_5\text{H}_{10}\), we can determine six isomers; from \(\text{C}_6\text{H}_{12}\), there are seventeen. Drawing these structures requires adding double bonds and branching differently to meet the formula while creating unique compounds.
alkene structural drawing
Drawing alkenes involves knowing where to place the double bonds and how to arrange carbon chains. For example:
  • Start with the longest chain of carbons.
  • Introduce the double bond(s) at the appropriate carbon(s).
  • Add branches and substituents based on the isomer being drawn.
For \(C_5H_{10}\), you’ll draw structures like 1-pentene, 2-pentene (both cis and trans forms), and branched isomers like 2-methyl-1-butene. These drawings help visualize isomers, crucial for understanding their different properties.

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Most popular questions from this chapter

Draw the structures for 1,4 -cyclohexadiene, \(1,3,5,7\)-cyclooctatetraene, 5 -methyl-1,3-cyclohexadiene, 2 -fluoro-1,3-cyclohexadiene, 3-bromo-1,4cycloheptadiene, and 1-bromo-1,4-cycloheptadiene.

Produce a bonding model for neutral methyl \(\left(\cdot \mathrm{CH}_{3}\right)\) using the unhybridized atomic orbitals of carbon and the hydrogen \(1 \mathrm{~s}\) orbitals. Critically discuss the shortcomings of this model. What's wrong with it?

Although you should be able to draw structures for the following compounds, they are named incorrectly. Give the correct systematic name for each compound: (a) 5 -chloro-2-methyl-6-vinyldecane (b) 3 -isopropyl-1-pentyne (c) 4-methyl-6-hepten-1-yne (d) \((E)-3\)-propyl-2, 5 -hexadiene

Find the compound of the formula \(\mathrm{C}_{10} \mathrm{H}_{16}\) that is composed of two six-membered rings and which has only three different carbons.

Find all the compounds of the formula \(\mathrm{C}_{4} \mathrm{H}_{6}\) in which there are four different carbon atoms. There are only nine compounds possible, but two of them may seem quite strange at this point. Hint: One of the strange molecules contains a carbon that is part of two double bonds, and the other is a compound containing only three-membered rings.
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