There are nine alkane constitutional isomers with the molecular formula C₇H₁₆. Draw them.

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Step 1: Understand the concept of constitutional isomers. Constitutional isomers are compounds with the same molecular formula but different connectivity of atoms. For the molecular formula C₇H₁₆, we are tasked with finding all possible unique structures where the carbon and hydrogen atoms are connected differently.

Step 2: Start with the simplest structure, the straight-chain alkane. Draw n-heptane, which is a linear chain of seven carbon atoms (C-C-C-C-C-C-C) with the appropriate number of hydrogens to satisfy the valency of carbon (4 bonds per carbon).

Step 3: Create branched isomers by shortening the main chain and adding methyl (CH₃) or ethyl (C₂H₅) groups as substituents. For example, draw a six-carbon chain (hexane) and add a methyl group at different positions to create isomers like 2-methylhexane and 3-methylhexane.

Step 4: Continue branching further. For example, create a five-carbon chain (pentane) and add two methyl groups at different positions to form isomers like 2,2-dimethylpentane and 2,3-dimethylpentane. Ensure that each structure is unique and does not repeat connectivity.

Step 5: Verify that you have drawn all nine isomers by systematically checking each possible branching pattern and ensuring no duplicates. Confirm that each structure adheres to the molecular formula C₇H₁₆ and satisfies the valency rules for carbon and hydrogen.

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Key Concepts

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

Alkanes

Alkanes are saturated hydrocarbons consisting only of carbon (C) and hydrogen (H) 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 relatively low reactivity and are commonly found in natural gas and petroleum.

Constitutional Isomers

Constitutional isomers are compounds that have the same molecular formula but differ in the connectivity of their atoms. This means that the arrangement of atoms in the molecule varies, leading to different structural forms. For C₇H₁₆, the nine constitutional isomers include straight-chain and branched forms, showcasing the diversity of structures possible with the same number of atoms.

Drawing Structural Formulas

Drawing structural formulas involves representing the arrangement of atoms in a molecule, including bonds between them. For alkanes, this means illustrating the carbon backbone and the hydrogen atoms attached to each carbon. Understanding how to depict these structures is essential for visualizing isomers and their unique properties.

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