The IUPAC nomenclature of the compound H$_3$C - CH(CH$_3$) - CH(CH$_3$) - CH$_2$ - CH$_3$

Analyze the question: We need the IUPAC name of CH₃–CH(CH₃)–CH(CH₃)–CH₂–CH₃.

Concept: To name an alkane:

1. Find the longest continuous carbon chain (this gives the parent name).
2. Number from the end that gives the substituents the lowest numbers.
3. Name and locate the branches.

Solution:

Write out the carbons:

• C1: CH₃
• C2: CH (with a CH₃ branch)
• C3: CH (with a CH₃ branch)
• C4: CH₂
• C5: CH₃

The longest chain is 5 carbons, so the parent is pentane.

Two methyl groups are attached, one on C2 and one on C3 (numbering from the left gives 2,3; numbering from the right would give 3,4, so we use 2,3).

Name: 2,3-dimethylpentane

Check the formula: 5 chain carbons + 2 methyl carbons = 7 carbons, so C₇H₁₆ (a heptane isomer). This matches option B.

The other options don't fit:

• A (3,4-dimethylhexane) has 8 carbons, which is too many.
• C (2-ethylhexane) is an incorrect name and has 8 carbons.
• D (2,3-dimethylhexane) has 8 carbons.

Answer: B. 2,3-dimethylpentane.

Tip: Always count the total carbons in the structure and compare them to the carbons in the proposed name (parent chain plus branches). That quickly eliminates wrong options.