Identify the product formed in the following reaction sequence.
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Reaction of alkyl halides with KCN increases the carbon chain by one carbon atom:
\[
R-X \rightarrow R-CN
\]
Reduction of nitriles gives primary amines:
\[
R-CN \rightarrow R-CH_2NH_2
\]
Thus, alkyl halide \(\rightarrow\) nitrile \(\rightarrow\) primary amine is a common method for chain extension.
Step 1: Write the structure of cyclopentyl chloride. Cyclopentyl chloride ($C_5H_9Cl$) is a five-membered carbocyclic ring with chlorine on one ring carbon. It is a secondary alkyl halide. Step 2: Reaction with ethanolic KCN. Alkyl halides react with potassium cyanide ($KCN$) in ethanol via nucleophilic substitution. The cyanide ion ($CN^-$) attacks through its carbon end, displacing $Cl^-$ and forming a nitrile (carbon chain extended by one): \[ C_5H_9Cl + KCN \xrightarrow{\text{ethanolic}} C_5H_9CN + KCl \] Product: cyclopentyl cyanide (cyclopentanecarbonitrile). Step 3: Identify the reducing agent for the nitrile. The nitrile is reduced using sodium amalgam ($Na/Hg$) in ethanol. Sodium amalgam provides nascent hydrogen, which adds stepwise across the $C \equiv N$ triple bond. Step 4: Write the reduction of nitrile to amine. \[ C_5H_9{-}C \equiv N \xrightarrow{Na/Hg,\ C_2H_5OH} C_5H_9{-}CH_2{-}NH_2 \] The nitrile carbon becomes $-CH_2NH_2$ (aminomethyl group). The product is a primary amine. Step 5: Name the product. The product has a cyclopentane ring attached to $-CH_2NH_2$. This is cyclopentylmethylamine (cyclopentanemethylamine), a primary amine. It has one more carbon than the starting alkyl chloride. Step 6: Understand the synthetic significance. The sequence $RCl \rightarrow RCN \rightarrow RCH_2NH_2$ is a useful method to extend the carbon chain by one and introduce a primary amino group. This illustrates the synthetic utility of KCN in organic chemistry. Step 7: State the final answer. \[ \boxed{\text{Cyclopentylmethylamine}\ (C_5H_9{-}CH_2{-}NH_2)} \]
