Question

The correct IUPAC name of the following compound is: \[ {CH3-CH2-CH(CH3)-CH2-CH(CH3)-CH2-CH3} \]

• A. 3-methyl-5-ethylhexane
• B. 3-ethyl-5-methylheptane
• C. 3,5-dimethylheptane
• D. 2,4-diethylhexane

Hint:

Choose the longest chain as parent and number it to give substituents the lowest possible locants.

Answer 1

The Correct Option is C

Step 1: Understanding the Topic:
The problem requires applying the IUPAC (International Union of Pure and Applied Chemistry) rules for naming branched-chain alkanes. Systematic nomenclature ensures that every organic molecule has a unique and descriptive name. The process involves identifying the longest continuous carbon chain, numbering it to give substituents the lowest possible positions, and arranging substituents in alphabetical order.
Step 2: Key Formulas and Approach:
The approach follows these rules:
Identify the longest carbon chain (parent chain).
Number the chain to give the substituents the lowest possible locants.
If two different substituents are at equivalent positions from either end, the one that comes first alphabetically gets the lower number.
Write the final name with substituents in alphabetical order.

Step 3: Detailed Explanation:

Longest Chain: By tracing the structure, we find a 7-carbon continuous chain. A 6-carbon "hexane" path exists, but it is not the longest. The parent name is thus heptane.
Substituents: There is a 1-carbon branch (methyl) and a 2-carbon branch (ethyl).
Numbering:
If we number from left-to-right: Ethyl is at position 3, Methyl is at position 5. (Locants: 3, 5).
If we number from right-to-left: Methyl is at position 3, Ethyl is at position 5. (Locants: 3, 5).

Tie-Breaker: Since both directions give the same locant set (3, 5), we apply alphabetical priority. "Ethyl" (E) comes before "Methyl" (M). Therefore, the ethyl group is prioritized with the lower number (3).
Assembly: The name is 3-ethyl-5-methylheptane.
Step 4: Final Answer:
The correct IUPAC name is 3-ethyl-5-methylheptane, matching option (A).