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Ch.12 Introduction to Organic Chemistry: Alkanes
McMurry - Fundamentals of General, Organic, and Biological Chemistry 8th Edition
McMurry8th EditionFundamentals of General, Organic, and Biological ChemistryISBN: 9780134015187Not the one you use?Change textbook
All textbooksMcMurry 8th EditionCh.12 Introduction to Organic Chemistry: AlkanesProblem 44b
Chapter 12, Problem 44b

How many straight-chain isomers can you write that fit the following descriptions? See Worked Example 12.12 for guidance.
b. Amines (―NH2) with a longest chain of 7 carbons

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Understand the problem: We are tasked with determining the number of straight-chain isomers of amines (compounds containing an ―NH₂ group) where the longest carbon chain has 7 carbons. Straight-chain means the carbon atoms are connected in a continuous, unbranched chain.
Step 1: Start by drawing the straight-chain structure of 7 carbons (heptane). This will serve as the backbone for all possible isomers.
Step 2: Place the ―NH₂ group (amino group) on each carbon atom of the 7-carbon chain, one at a time. Remember that the position of the ―NH₂ group on the chain determines a unique isomer.
Step 3: Consider symmetry in the molecule. For example, placing the ―NH₂ group on carbon 1 is equivalent to placing it on carbon 7 due to the symmetry of the straight chain. Eliminate duplicate structures caused by symmetry.
Step 4: Count the unique positions of the ―NH₂ group on the 7-carbon chain after accounting for symmetry. Each unique position corresponds to a distinct isomer.

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Key Concepts

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

Straight-Chain Isomers

Straight-chain isomers are compounds that have the same molecular formula but differ in the arrangement of their carbon atoms in a linear fashion. In the context of amines, these isomers will have variations in the positioning of the amine group (―NH₂) along the carbon chain, leading to different structural forms while maintaining the same number of carbon atoms.
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Isomers Concept 1

Amines

Amines are organic compounds derived from ammonia (NH₃) by replacing one or more hydrogen atoms with alkyl or aryl groups. In this case, the presence of the amine functional group (―NH₂) is crucial for identifying the isomers, as it influences the chemical properties and reactivity of the compounds formed from the carbon chain.
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Amine Classification Example 1

Longest Carbon Chain

The longest carbon chain in a molecule refers to the maximum continuous sequence of carbon atoms connected by single bonds. For the purpose of identifying isomers, determining the longest chain is essential, as it establishes the backbone of the molecule and dictates the possible variations in the structure of the amine isomers based on the placement of the amine group.
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Related Practice
Textbook Question

Give an example of a compound that meets the following descriptions:

b. A cycloalkane with three substituents

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Textbook Question

If one compound has the formula C5H10 and another has the formula C4H10 are the two compounds isomers? Explain.

Textbook Question

What is wrong with the following structures?

a. CH3=CHCH2CH2OH

Textbook Question

Which of the following pairs of structures are identical, which are isomers, and which are unrelated?

a.

Textbook Question

How many isomers can you write that fit the following descriptions? See Worked Example 12.12 for guidance.

c. Alcohols (―OH) formed from 2-methylhexane

Textbook Question

Write condensed structures for the following molecular formulas. More than one isomer will be required for each.

a. Isomers of C8H18 that contain two methyl groups and a longest chain of 4 carbons