Question

What tests could you perform to distinguish between the following pairs of compounds?

_{$$\begin{gathered} {\mathbf{\text{a.CH}}}_{\mathbf{\text{3}}}{\mathbf{\text{CH}}}_{\mathbf{\text{2}}}{\mathbf{\text{CH}}}_{\mathbf{\text{2}}}{\mathbf{\text{CH}}}_{\mathbf{\text{3}}}{\mathbf{\text{,CH}}}_{\mathbf{\text{2}}}{\mathbf{\text{= CHCH}}}_{\mathbf{\text{2}}}{\mathbf{\text{CH}}}_{\mathbf{\text{3}}} \\ {\mathbf{\text{b.CH}}}_{\mathbf{\text{3}}}{\mathbf{\text{CH}}}_{\mathbf{\text{2}}}{\mathbf{\text{CH}}}_{\mathbf{\text{2}}}{\mathbf{\text{COOH}}}_{\mathbf{\text{,}}}{\mathbf{\text{,CH}}}_{\mathbf{\text{3}}}{\mathbf{\text{CH}}}_{\mathbf{\text{2}}}{\mathbf{\text{CCH}}}_{\mathbf{\text{3}}} \\ {\mathbf{\text{c.CH}}}_{\mathbf{\text{3}}}{\mathbf{\text{CH}}}_{\mathbf{\text{2}}}{\mathbf{\text{CH}}}_{\mathbf{\text{2}}}{\mathbf{\text{OH}}}_{\mathbf{\text{4}}}{\mathbf{\text{,CH}}}_{\mathbf{\text{3}}}{\mathbf{\text{CH}}}_{\mathbf{\text{3}}} \\ {\mathbf{\text{d.CH}}}_{\mathbf{\text{3}}}{\mathbf{\text{CH}}}_{\mathbf{\text{2}}}{\mathbf{\text{NH}}}_{\mathbf{\text{2}}}{\mathbf{\text{,CH}}}_{\mathbf{\text{3}}}{\mathbf{\text{OCH}}}_{\mathbf{\text{3}}} \end{gathered}$$}

Short answer

(a) The difference between alkane and alkene in the bromine test would be how they react with bromine.

(b) $2,4$-Dinitrophenylhydrazine

(c)We can carry on oxidation or add$2,4$-dinitrophenylhydrazine

(d) To be able to distinguish the two, both should be dissolved in water. While the dissolution of${\text{CH}}_{\text{3}}{\text{CH}}_{\text{2}}{\text{NH}}_{\text{2}}$ should have a basic pH, the dissolution of${\text{CH}}_{\text{3}}{\text{OCH}}_{\text{3}}$ will not.

Step-by-step solution

Step 1: CH3CH2CH2CH3,CH2 = CHCH2CH3

In order to differrntiate between the given compounds,

we will use the bromine test.

When bromine is dissolved, the solution will be coloured red, because bromine gives that color.

Since we know that bromine will react with alkenes but stay neutral to alkanes.

Therefore, when we add to the given alkene the bromine solution, they will react and bromine will be added to the alkene.

This will make the solution transparent. If we add an alkane to the bromine solution, the solution will stay coloured red, since alkane wont react with bromine.

Hence, the difference between alkene and alkane in this test would be how they react with bromine.

Hence The difference between alkane and alkene in bromine test would be how they react with bromine.

CH3CH2CH2COOH,,CH3CH2CCH3

$2,4$-Dinitrophenylhydrazine reacts with ketones but not with carboxylic acids.

The reaction of ketone and 2,4 -DNPH is a condensation reaction which yields the corresponding hydrazone. The hydrazine is usually a brightly colored yellow, orange, or red compound, so the reaction is often used to test for the presences of an aldehyde or ketone

2,4 -DNPH does not react with carboxylic acids because the carbonyl carbon of carboxylic acids is less electrophilic, and consequently attack by the nucleophilic 2,4-DNPH is less favored.

Hence 2,4 -Dinitrophenylhydrazine

Step 3: CH3CH2CH2OH4,CH3CH3

We can perform two types of tests in this case. The first one is the addition of

2,4-dinitrophenylhydrazine where ketone will form an orange precipitate, while there will be no reaction with alcohol.

The second test is to perform an oxidation. Ketone will not react and primary alcohol will be oxidized into aldehyde and carboxylic acid.

Hence We can carry on oxidation or add 2,4-dinitrophenylhydrazine

Step 4: .CH3CH2NH2,CH3OCH3

To be able to distinguish between the two compounds${\text{CH}}_{\text{3}}{\text{CH}}_{\text{2}}{\text{NH}}_{\text{2}}{\text{,andCH}}_{\text{3}}{\text{OCH}}_{\text{3}}$ we must identify what type of hydrocarbon cach compound is. Once we identify this, it will be easier for us to know which tests suit best to distinguish the compounds.

We can identify${\text{CH}}_{\text{3}}{\text{CH}}_{\text{2}}\text{NH}$ as an amine, thus it should behave as a base n water. The other compound,${\text{CH}}_{\text{3}}{\text{OCH}}_{\text{3}}$ is an ether hence, it will not behave as base in water.

Hence To be able to distinguish the two, both should be dissolved in water. While the dissolution of${\text{CH}}_{\text{3}}{\text{CH}}_{\text{2}}{\text{NH}}_{\text{2}}$ should have a basic pH, the dissolution of${\text{CH}}_{\text{3}}{\text{OCH}}_{\text{3}}$ will not.