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

Verified step by step guidance

1. Step 1: Understand the molecular formula C₈H₁₈. This is an alkane (saturated hydrocarbon) with 8 carbon atoms and 18 hydrogen atoms. The general formula for alkanes is CₙH₂ₙ₊₂, which confirms this is a valid alkane.
2. Step 2: Recognize that the problem specifies isomers with a longest chain of 4 carbons. This means the main chain (parent chain) will have 4 carbons, and the remaining carbons will be arranged as substituents (methyl groups).
3. Step 3: Place the two methyl groups (-CH₃) on different carbons of the 4-carbon chain to create structural isomers. For example, you can place both methyl groups on the same carbon, or distribute them across different carbons in the chain.
4. Step 4: Write the condensed structural formulas for each isomer. For example, one isomer could have both methyl groups on the second carbon of the chain, written as CH₃C(CH₃)₂CH₂CH₃. Another isomer could have one methyl group on the second carbon and the other on the third carbon, written as CH₃CH(CH₃)CH(CH₃)CH₃.
5. Step 5: Verify that each structure adheres to the molecular formula C₈H₁₈ and that no duplicate structures are included. Ensure all possible unique arrangements of the two methyl groups on the 4-carbon chain are considered.

Key Concepts

Isomers

Isomers are compounds that have the same molecular formula but differ in the arrangement of atoms. This can lead to variations in chemical properties and structures. In the case of C₈H₁₈, isomers can be structural, where the connectivity of atoms changes, or stereoisomers, where the spatial arrangement differs.

Condensed Structures

Condensed structures are a way of representing molecular formulas that show the connectivity of atoms without depicting all the bonds explicitly. They provide a simplified view of the molecule, making it easier to visualize the arrangement of atoms, especially in larger molecules like isomers of C₈H₁₈.

Longest Chain

The longest chain in a hydrocarbon refers to the maximum continuous sequence of carbon atoms in a molecule. Identifying the longest chain is crucial for naming and classifying isomers, as it determines the base name of the compound. In this case, the longest chain of 4 carbons is essential for constructing the isomers of C₈H₁₈ with two methyl groups.