Name this molecule: CH3CH(CH3)CH3

Name this molecule: CH3CH(CH3)CH3

• A. Pentane
• B. Methylpropane
• C. Ethane
• D. Propane

Answer: (B)

Naming branched alkanes involves choosing the longest continuous carbon chain as the base and then naming any substituent groups with their positions. In this molecule, there are four carbons in total, but the longest chain you can trace is three carbons, so the base name is propane. There is a single methyl group attached to the second carbon of that chain, giving a methyl substituent at position 2. So the name is 2-methylpropane. This is the same compound commonly called methylpropane (also known as isobutane). It’s not pentane, since five carbons would be needed in the main chain, and it’s not ethane or propane because the structure includes that methyl substituent on a propane backbone.

Naming branched alkanes involves choosing the longest continuous carbon chain as the base and then naming any substituent groups with their positions. In this molecule, there are four carbons in total, but the longest chain you can trace is three carbons, so the base name is propane. There is a single methyl group attached to the second carbon of that chain, giving a methyl substituent at position 2. So the name is 2-methylpropane. This is the same compound commonly called methylpropane (also known as isobutane). It’s not pentane, since five carbons would be needed in the main chain, and it’s not ethane or propane because the structure includes that methyl substituent on a propane backbone.