For any symmetric product of a Wurtz reaction, count the total number of carbons and divide by 2 to get the chain size of the reactant. The product has 12 carbons total, so reactant 'A' must have exactly 6 carbons. All options have 6 carbons, but splitting the structure evenly reveals a tertiary carbon attachment, pointing safely to option (A).
Step 1: Understanding the Question:
We need to determine the starting alkyl halide 'A' that undergoes a standard Wurtz reaction (using sodium metal in dry ether) to yield the symmetrical alkane dimer, 3,4-diethyl-3,4-dimethylhexane.
Step 2: Key Formula or Approach:
The Wurtz reaction involves the coupling of two identical alkyl radical fragments:
$$ 2\text{R-X} + 2\text{Na} \xrightarrow{\text{dry ether}} \text{R-R} + 2\text{NaX} $$
To find the structure of the starting alkyl radical (R), we look at the symmetrical product molecule (R-R), locate its central line of structural symmetry, split it exactly into two identical halves, and attach a halogen atom (Cl) to the carbon that was joined at the symmetry line.
Step 3: Detailed Explanation:
Let's first draw and analyze the carbon chain structure of the given product, 3,4-diethyl-3,4-dimethylhexane:
$$ \text{CH}_3-\text{CH}_2-\text{C}(\text{CH}_3)(\text{C}_2\text{H}_5)-\text{C}(\text{CH}_3)(\text{C}_2\text{H}_5)-\text{CH}_2-\text{CH}_3 $$
Dividing this symmetrical molecule perfectly in half across the central $\text{C}_3-\text{C}_4$ carbon-carbon single bond gives two identical fragments of the alkyl radical R:
$$ \text{CH}_3-\text{CH}_2-\text{C}(\text{CH}_3)(\text{CH}_2\text{CH}_3)- $$
Attaching a chlorine atom to the radical junction point yields the parent alkyl halide compound 'A':
$$ \text{CH}_3-\text{CH}_2-\text{C(Cl)}(\text{CH}_3)-\text{CH}_2-\text{CH}_3 $$
To determine its official IUPAC name:
1. The longest continuous carbon chain containing the functional group contains 5 carbons (a pentane backbone).
2. Numbering from either side gives substituents at carbon position 3.
3. At carbon-3, there is both a chloro group and a methyl group.
Arranging alphabetically gives: 3-Chloro-3-methylpentane.
Step 4: Final Answer:
The correct starting material is 3-Chloro-3-methylpentane, matching option (A).
