The Wurtz reaction is a coupling reaction where two alkyl halides react with sodium metal in dry ether to form a higher alkane. The general reaction is:

$2 R - X + 2 Na \to R - R + 2 NaX$

When only one type of alkyl halide is used, the product is a symmetrical alkane (with an even number of carbon atoms). To synthesize an unsymmetrical alkane (with different alkyl groups), a mixture of two different alkyl halides must be used. However, this often leads to a mixture of three products (R-R, R-R', and R'-R') due to cross-coupling, making it inefficient for pure unsymmetrical alkane synthesis.

Specifically, the compound that cannot be synthesized by the Wurtz reaction using only one type of halide is an unsymmetrical alkane. For example, propane (CH₃-CH₂-CH₃) has an odd number of carbon atoms (3) and is unsymmetrical. It cannot be formed from a single alkyl halide because that would only produce symmetrical alkanes like ethane (from CH₃I) or butane (from CH₃CH₂I). Propane would require a cross-coupling between methyl iodide and ethyl iodide, but even then, a mixture of ethane, propane, and butane is obtained.

Looking at the options (which are images not rendered here, but typically include structures like propane, butane, etc.), the compound with an odd number of carbon atoms (like propane) or any unsymmetrical alkane is the one that cannot be synthesized using one type of halide only.

Related Topics & Formulae

Wurtz Reaction: Used for preparing higher alkanes containing even number of carbon atoms from alkyl halides. Limited to symmetrical alkanes when using a single halide.

Symmetrical vs. Unsymmetrical Alkanes: Symmetrical alkanes have identical groups on both ends (e.g., CH₃-CH₃), while unsymmetrical have different groups (e.g., CH₃-CH₂-CH₃).

Alternative Methods: For unsymmetrical alkanes, other reactions like Wurtz-Fittig (using aryl halide and alkyl halide) or Corey-House synthesis are preferred to avoid mixture issues.