To name these alkanes correctly, we follow a few simple rules:
1.
Find the longest chain of carbon atoms connected in a row. This is the "parent" chain.
2.
Number the chain starting from the end that gives the branches (groups sticking off) the lowest possible numbers.
3.
Identify the branches:
* A 1-carbon branch is called
methyl.
* A 2-carbon branch is called
ethyl.
4.
Put it all together: List the branches in alphabetical order (ethyl before methyl), use prefixes like *di-* if there are two of the same branch, and add the parent name at the end.
Here is the step-by-step solution for each problem:
1.
*
Longest Chain: 5 carbons $\rightarrow$ Pentane.
*
Branches: Two methyl groups on carbon #2.
*
Name: 2,2-dimethylpentane.
2.
*
Longest Chain: 5 carbons $\rightarrow$ Pentane.
*
Branches: One methyl group on carbon #3.
*
Name: 3-methylpentane.
3.
*
Longest Chain: 5 carbons $\rightarrow$ Pentane.
*
Branches: One ethyl group on carbon #3.
*
Name: 3-ethylpentane.
4.
*
Longest Chain: 6 carbons $\rightarrow$ Hexane.
*
Branches: An ethyl group and a methyl group both on carbon #3.
*
Alphabetical Order: Ethyl comes before Methyl.
*
Name: 3-ethyl-3-methylhexane.
5.
*
Longest Chain: 7 carbons $\rightarrow$ Heptane.
*
Branches: An ethyl group and a methyl group both on carbon #4.
*
Alphabetical Order: Ethyl comes before Methyl.
*
Name: 4-ethyl-4-methylheptane.
6.
*
Longest Chain: 8 carbons $\rightarrow$ Octane.
*
Branches: An ethyl group and a methyl group both on carbon #4.
*
Alphabetical Order: Ethyl comes before Methyl.
*
Name: 4-ethyl-4-methyloctane.
7.
*
Longest Chain: 9 carbons $\rightarrow$ Nonane.
*
Branches: An ethyl group and a methyl group both on carbon #5.
*
Alphabetical Order: Ethyl comes before Methyl.
*
Name: 5-ethyl-5-methylnonane.
Final Answer:
1. 2,2-dimethylpentane
2. 3-methylpentane
3. 3-ethylpentane
4. 3-ethyl-3-methylhexane
5. 4-ethyl-4-methylheptane
6. 4-ethyl-4-methyloctane
7. 5-ethyl-5-methylnonane
Parent Tip: Review the logic above to help your child master the concept of alkanes worksheet.
