Question

An alkane ${C_7}{H_{16}}$ is produced by the reaction of lithium di(3-pentyl)cuprate with ethyl bromide. The name of the product is:
A. 3-methylhexane
B. 2-ethylpentane
C. 3-ethylpentane
D. n-heptane

Answer 1

Hint: The lithium di(3-pentyl)cuprate is commonly known as Gilman reagent which is used for coupling reaction. On reacting with ethyl bromide carbon-carbon bond is formed by replacing the halogen of ethyl bromide with alkyl group. In this reaction nucleophilic substitution reaction takes place where the Gilman reagent acts as a nucleophile.

Complete step by step answer:
Lithium di(3-pentyl)cuprate is known as Gilman reagent. The Lithium di(3-pentyl)cuprate is formed by reacting organolithium reagent with cuprous iodide. Gilman reagents act as a carbanion. The lithium di(3-pentyl)cuprate (Gilman reagent) gives coupling reaction with alkyl halide. In the reaction of lithium di(3-pentyl)cuprate (Gilman reagent) with alkyl halide, results in the replacement of halogen atom by a alkyl group to form carbon-carbon bond of hydrocarbon alkane, lithium halide and alkyl copper.
In this question, lithium di(3-pentyl)cuprate reacts with ethyl bromide to form an alkane as a main product because of carbon-carbon coupling.
The reaction of lithium di(3-pentyl)cuprate reacts with ethyl bromide is shown below.
${[{(C{H_3}C{H_2})_2}CH]_2}CuLi + BrC{H_2}C{H_3} \to {C_2}{H_5} - CH({C_2}{H_5}) - {C_2}{H_5} + {(C{H_3}C{H_2})_2}CHCu + LiBr$
In this reaction, lithium di(3-pentyl)cuprate reacts with ethyl bromide to form 3-ethyl pentane as a main product, pentan-3-yl copper and lithium bromide.
The Gilman reagent acts as a nucleophile for nucleophilic substitution reaction ${S_N}2$ reaction.
Thus, the name of alkane ${C_7}{H_{16}}$ produced by the reaction of lithium di(3-pentyl)cuprate with ethyl bromide is 3-ethyl pentane.
Therefore, the correct option is C.

Note:
The Gilman reagent lithium di(3-pentyl)cuprate gives contrast property with the Grignard reagent. The alkyl halide on reacting with Grignard reagent gives very less quantity of the desired product as compared to Gilman reagent.