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Ch.3 - Structure and Stereochemistry of Alkanes
Wade - Organic Chemistry 9th Edition
Wade9th EditionOrganic ChemistryISBN: 9780135213728Not the one you use?Change textbook
All textbooksWade 9th EditionCh.3 - Structure and Stereochemistry of AlkanesProblem 33a
Chapter 3, Problem 33a

a. There are 18 isomeric alkanes of molecular formula C8H18. Draw and name any eight of them.

Verified step by step guidance
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Step 1: Understand the concept of isomerism. Isomers are compounds with the same molecular formula but different structural arrangements. In alkanes, isomerism arises due to different branching patterns.
Step 2: Start with the simplest structure, the straight-chain alkane. For C8H18, this is n-octane. Draw a linear chain of eight carbon atoms, each bonded to sufficient hydrogen atoms to satisfy the tetravalency of carbon.
Step 3: Create branched isomers by rearranging the carbon atoms. Begin by shortening the main chain and adding branches. For example, draw 2-methylheptane by having a seven-carbon chain with a methyl group (CH3) attached to the second carbon.
Step 4: Continue creating isomers by varying the position and number of branches. For instance, draw 3-methylheptane, 2,2-dimethylhexane, and 2,3-dimethylhexane. Ensure each structure has eight carbon atoms and eighteen hydrogen atoms.
Step 5: Name each isomer according to IUPAC nomenclature rules. Identify the longest carbon chain, number the chain to give the lowest numbers to the substituents, and list substituents alphabetically. Verify that each name corresponds to a unique structure.

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Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

Isomerism

Isomerism refers to the phenomenon where compounds have the same molecular formula but different structural arrangements. In organic chemistry, structural isomers differ in the connectivity of atoms, leading to variations in physical and chemical properties. Understanding isomerism is crucial for identifying and drawing different isomeric forms of a given compound.
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Alkanes

Alkanes are saturated hydrocarbons consisting solely of carbon and hydrogen atoms, connected by single bonds. They follow the general formula CnH2n+2, where n is the number of carbon atoms. Alkanes are characterized by their lack of reactivity due to the stability of C-C and C-H bonds, making them a fundamental class of compounds in organic chemistry.
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IUPAC Nomenclature

IUPAC nomenclature is a standardized system for naming chemical compounds, ensuring clarity and consistency in communication. For alkanes, the name is derived from the longest carbon chain, with prefixes indicating the presence and position of branches or substituents. Mastery of IUPAC rules is essential for accurately naming and identifying different isomers.
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Related Practice
Textbook Question

Which of the following structures represent the same compound? Which ones represent different compounds?

(b)

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Textbook Question

Name the following compounds.

(c)

(d)

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Textbook Question

Draw and name the six isomeric cyclopentanes of molecular formula C7H14. These will include four constitutional isomers, of which two show geometric (cis-trans) stereoisomerism.

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Textbook Question

Use your models to do a chair–chair interconversion on each ring of the conformation of cis-decalin shown in Figure 3-27. Draw the conformation that results.

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Textbook Question

Which of the following structures represent the same compound? Which ones represent different compounds?

(a)

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Textbook Question

Name the following compounds.

(a)

(b)

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