Chapter 11: Problem 12
Among the 18 structural isomers with the formula \(\mathrm{C}_{8} \mathrm{H}_{18}\) are two with a five-carbon chain having one ethyl and one methyl substituent group. Draw the structures and name these two isomers.
Short Answer
Expert verified
The two isomers are 3-Ethyl-2-methylpentane and 2-Ethyl-3-methylpentane.
Step by step solution
01
Understanding the Problem
We need to find two structural isomers of octane (\(C_8H_{18}\)) that have five carbon atoms in their main chain, with one ethyl and one methyl as substituents. A structural isomer has the same molecular formula but a different arrangement of atoms.
02
Constructing the Main Chain
Since the isomers need a five-carbon main chain, we draw a straight chain with five carbon atoms: \(C-C-C-C-C\). This forms the backbone of each isomer.
03
Placing the Ethyl Group
An ethyl group \((C_2H_5)\) consists of two carbon atoms. It can be attached to the second or third carbon of the main chain to create different isomers. We avoid the first and last carbon to maintain the five-carbon chain.
04
Placing the Methyl Group
A methyl group \((CH_3)\) consists of one carbon atom. It also needs to be attached to the main chain. We place it on the remaining available carbons to form a valid structure.
05
Drawing the First Isomer
In the first possibility, place the ethyl group on the second carbon and the methyl group on the third carbon. This gives the structure: \(\begin{array}{c} \text{CH}_3-\text{CH}(\text{C}_2\text{H}_5)-\text{CH}(\text{CH}_3)-\text{CH}_2-\text{CH}_3 \end{array}\).
06
Naming the First Isomer
Using the IUPAC naming system, the name for this structure is 3-Ethyl-2-methylpentane. Here '3-ethyl' indicates the ethyl group is on the third carbon, and '2-methyl' indicates the methyl group is on the second carbon.
07
Drawing the Second Isomer
In the second possibility, place the ethyl group on the third carbon and the methyl group on the second carbon. This gives the structure: \(\begin{array}{c} \text{CH}_3-\text{CH}(\text{CH}_3)-\text{CH}(\text{C}_2\text{H}_5)-\text{CH}_2-\text{CH}_3 \end{array}\).
08
Naming the Second Isomer
Using IUPAC naming, the name for the second structure is 2-Ethyl-3-methylpentane, where '2-ethyl' indicates the ethyl group is on the second carbon, and '3-methyl' indicates the methyl group is on the third carbon.
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Key Concepts
These are the key concepts you need to understand to accurately answer the question.
Octane
Octane is a simple hydrocarbon, commonly known and referred to due to its significance in fuel ratings, like gasoline. It consists of 8 carbon atoms and 18 hydrogen atoms, formulaically represented as \( C_8H_{18} \).
In organic chemistry, octane is known for having several structural isomers.
These isomers have the same molecular formula but different structures, leading to varying properties.
Structural isomers can affect fuel efficiency and the environmental impact of emissions.
In organic chemistry, octane is known for having several structural isomers.
These isomers have the same molecular formula but different structures, leading to varying properties.
- For example, these differences are observed in their boiling points and calculated octane ratings in fuels.
- Octane ratings indicate a fuel's capacity to resist knocking during combustion—a desirable trait for efficient engine performance.
Structural isomers can affect fuel efficiency and the environmental impact of emissions.
IUPAC naming
The IUPAC naming system is a standard method for naming organic compounds.
It allows chemists across the globe to communicate compounds' structures unambiguously.
The first step in IUPAC naming is identifying the longest continuous carbon chain.
This chain forms the base of the compound's name.
It’s not just a tool for categorization, but a universal language in organic chemistry.
It allows chemists across the globe to communicate compounds' structures unambiguously.
The first step in IUPAC naming is identifying the longest continuous carbon chain.
This chain forms the base of the compound's name.
- Substituents, like ethyl or methyl groups, are then identified and named accordingly.
- These groups are arranged in the name based on their position and alphabetical order.
- Numbering of the carbon chain starts from the end closest to the substituent with the highest alphabetical order.
It’s not just a tool for categorization, but a universal language in organic chemistry.
Carbon chain
A carbon chain refers to a series of carbon atoms bonded together, forming the backbone of organic molecules.
These chains can be linear, branched, or even cyclic.
This subtle rearrangement results in a different compound, showing the versatility and complexity that carbon chains bring to organic chemistry.
These chains can be linear, branched, or even cyclic.
- In hydrocarbons like octane, the carbon chain is a crucial aspect, dictating both the compound's properties and its name.
- The length and structure of the carbon chain play a key role in determining boiling point, stability, and reactivity of the molecule.
This subtle rearrangement results in a different compound, showing the versatility and complexity that carbon chains bring to organic chemistry.
Organic chemistry
Organic chemistry is the study of carbon-containing compounds, including octane and its isomers.
It's a vast field, covering everything from simple molecules like methane to extensive chains and rings found in complex biomolecules.
The work involves understanding how carbon forms stable bonds with itself and other elements like hydrogen, oxygen, and nitrogen.
It's a vast field, covering everything from simple molecules like methane to extensive chains and rings found in complex biomolecules.
The work involves understanding how carbon forms stable bonds with itself and other elements like hydrogen, oxygen, and nitrogen.
- Organic chemistry investigates reactions between these compounds—how they form, interact, and transform.
- It focuses on functional groups and the formation of complex architectures, like benzene rings and large polymers.
- In real-world applications, knowledge of organic chemistry aids in creating pharmaceuticals, materials, fuels, and more.