Give reactions for tests that can be carried out rapidly in...

Give reactions for tests that can be carried out rapidly in a test tube to differentiate the following compounds: hexane, $\mathrm{CH}_3 \mathrm{CH}=\mathrm{CHCl}, \mathrm{H}_2 \mathrm{C}=\mathrm{CHCH}_2 \mathrm{Cl}$ and $\mathrm{CH}_3 \mathrm{CH}_2 \mathrm{CH}_2 \mathrm{Cl}$. Hexane is readily distinguished from the other three compounds because there is a negative test for $\mathrm{Cl}^{-}$after $\mathrm{Na}^{-}$ fusion and treatment with acidic $\mathrm{AgNO}_3$. The remaining three compounds are differentiated by their reactivity with alcoholic $\mathrm{AgNO}_3$ solution. $\mathrm{CH}_3 \mathrm{CH}=\mathrm{CHCl}$ is a vinylic chloride and does not react even on heating. $\mathrm{H}_2 \mathrm{C}=\mathrm{CHCH} \mathrm{Cl}_2$ is most reactive (allylic) and precipitates $\mathrm{AgCl}$ in the cold, while $\mathrm{CH}_3 \mathrm{CH}_2 \mathrm{CH}_2 \mathrm{Cl}$ gives a precipitate of $\mathrm{AgCl}$ on warming with the reagent.

Give reactions for tests that can be carried out rapidly in a test tube to differentiate the following compounds: hexane, $\mathrm{CH}_3 \mathrm{CH}=\mathrm{CHCl}, \mathrm{H}_2 \mathrm{C}=\mathrm{CHCH}_2 \mathrm{Cl}$ and $\mathrm{CH}_3 \mathrm{CH}_2 \mathrm{CH}_2 \mathrm{Cl}$.

Hexane is readily distinguished from the other three compounds because there is a negative test for $\mathrm{Cl}^{-}$after $\mathrm{Na}^{-}$ fusion and treatment with acidic $\mathrm{AgNO}_3$. The remaining three compounds are differentiated by their reactivity with alcoholic $\mathrm{AgNO}_3$ solution. $\mathrm{CH}_3 \mathrm{CH}=\mathrm{CHCl}$ is a vinylic chloride and does not react even on heating. $\mathrm{H}_2 \mathrm{C}=\mathrm{CHCH} \mathrm{Cl}_2$ is most reactive (allylic) and precipitates $\mathrm{AgCl}$ in the cold, while $\mathrm{CH}_3 \mathrm{CH}_2 \mathrm{CH}_2 \mathrm{Cl}$ gives a precipitate of $\mathrm{AgCl}$ on warming with the reagent.

Key Concepts

Sodium Fusion Test

This test, also known as the Lassa test, involves the fusion of an organic compound with sodium metal to convert covalently bound halogens into soluble ionic halides. The resulting mixture is then treated with reagents such as silver nitrate to precipitate the halide as an insoluble salt. This procedure is crucial for detecting the presence of halogens in organic compounds, thereby differentiating between halogenated and non-halogenated substances.

Silver Nitrate Precipitation Test

The silver nitrate test is used to identify halide ions by forming insoluble silver halide precipitates. When a solution of silver nitrate is added to a halide-containing sample, the reaction produces a visible precipitate if halides are present. The effectiveness of the test and the conditions under which precipitation occurs can be manipulated by changing factors like the solvent (e.g., alcoholic or aqueous) and temperature, providing insights into the nature of the halide group in the organic molecule.

Structure-Dependent Reactivity of Organic Halides

The reactivity of organohalides in substitution reactions is highly influenced by the type and position of the halogen atom attached to the carbon skeleton. Factors such as whether the halogen is attached to a saturated carbon (alkyl halide), adjacent to a double bond (allylic halide), or directly attached to a double bond (vinylic halide) determine the ease with which these compounds react under different conditions. This concept is essential in understanding and predicting the behavior of various organic halides during diagnostic tests.

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