Identify the starting compound \(P\) in the following reaction.
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In Wurtz reaction, identify the alkyl halide by splitting the product at the newly formed central C-C bond. Each half corresponds to the alkyl group of the original alkyl halide.
The reagent sodium metal in dry ether is the classic signal for a Wurtz reaction, where two molecules of an alkyl halide join together at the carbon that used to carry the halogen, releasing sodium halide in the process.
Looking at the coupled product, $(CH_3)_2CHCH_2CH_2CH(CH_3)_2$, notice that it is perfectly symmetric about its central $-CH_2-CH_2-$ bond. Splitting the molecule right down the middle of that bond regenerates two identical fragments, each one being $(CH_3)_2CHCH_2-$, the isobutyl group.
Since Wurtz coupling simply joins two molecules of the same alkyl halide, the starting material P must be the bromide of this isobutyl fragment, $(CH_3)_2CHCH_2Br$, whose IUPAC name is 1-Bromo-2-methylpropane.
Coupling two molecules of this bromide over sodium in dry ether reforms the given product with loss of NaBr, confirming the identification. The correct choice is option (1).
