Question

The IUPAC name of $\text{CH}_3\text{-CH}_2\text{-CH(CH}_3\text{)-CH}_3$ is

• A. 2-Methylbutane
• B. Isopentane
• C. Pentane
• D. 3-Methylbutane

Hint:

Always identify the longest carbon chain and number any substituents from that chain, ensuring the lowest numbers are used for correct nomenclature.

Answer 1

The Correct Option is A

Step 1: Draw the chain.
The compound is $\text{CH}_3\text{-CH}_2\text{-CH(CH}_3)\text{-CH}_3$. We need its IUPAC name. First we find the longest carbon chain.
Step 2: Count the main chain.
The longest straight chain of carbons has four carbons in a row. A four carbon chain is named butane.
Step 3: Find the branch.
There is one extra $\text{CH}_3$ group sticking out. This branch is a methyl group.
Step 4: Number the chain.
We number from the end that gives the branch the smallest number. Counting that way, the methyl branch is on carbon 2.
Step 5: Build the name.
We put the position, then the branch, then the main chain. This gives 2-methylbutane.
Step 6: Rule out the others.
Isopentane is the old common name, not the IUPAC name. Pentane is a five carbon straight chain, which is wrong. 3-methylbutane is wrong because the lower number 2 must be used.\[ \boxed{\text{2-Methylbutane}} \]