Chapter 21, Problem 66E

(a)

Interpretation Introduction

Interpretation: The test to distinguish ${\text{CH}}_{\text{3}}{\text{CH}}_{\text{2}}{\text{CH}}_{\text{2}}{\text{CH}}_{\text{3}}$ and ${\text{CH}}_2{\text{=CHCH}}_{\text{2}}{\text{CH}}_{\text{3}}$ needs to be explained.

Concept Introduction : Alkenes can be distinguished from alkanes by reacting with halogens. If bromine halogen is used, the red colour of bromine will go away when it undergoes reaction with alkene but in case of alkane, the red colour of bromine remain exists.

Answer to Problem 66E

  ${\text{CH}}_{\text{3}}{\text{CH}}_{\text{2}}{\text{CH}}_{\text{2}}{\text{CH}}_{\text{3}}$ can be distinguished between ${\text{CH}}_2{\text{=CHCH}}_{\text{2}}{\text{CH}}_{\text{3}}$ by reacting with halogens ( ${\text{Cl}}_{\text{2}}$ or ${\text{Br}}_{\text{2}}$ ).

Explanation of Solution

When bromine adds to alkene, the red colour of bromine lost due to boning of bromine to alkene. This is an indication of alkene.

The reaction is as follows:

  

But on addition of bromine to alkane, its red colour will not no away.

(b)

Interpretation Introduction

Interpretation: The test to distinguish ${\text{CH}}_{\text{3}}{\text{CH}}_{\text{2}}{\text{CH}}_{\text{2}}\text{COOH}$ and needs to be explained.

Concept Introduction : Carboxylic acid can be distinguished from ketone by reacting with neutral ${\text{FeCl}}_{\text{3}}$ solution. Ketone does not give this test but carboxylic acid produces coloured precipitate.

Answer to Problem 66E

  ${\text{CH}}_{\text{3}}{\text{CH}}_{\text{2}}{\text{CH}}_{\text{2}}\text{COOH}$ can be distinguished from by reacting with neutral ${\text{FeCl}}_{\text{3}}$ solution.

Explanation of Solution

On reaction of butanoic acid with neutral ${\text{FeCl}}_{\text{3}}$ solution, it will give coloured ppt. The reaction is shown below.

  $\begin{array}{l}$ {\text{CH}}_{\text{3}}{\text{CH}}_{\text{2}}{\text{CH}}_{\text{2}}{\text{COOH + FeCl}}_3\to {({\text{CH}}_{\text{3}}{\text{CH}}_{\text{2}}\text{COO})}_3\text{Fe+3HCl}$\text{Butanoic}\text{acid}\text{ppt}\end{array}$

But ketone does not show this test.

(c)

Interpretation Introduction

Interpretation: The test that distinguishes ${\text{CH}}_{\text{3}}{\text{CH}}_{\text{2}}{\text{CH}}_{\text{2}}\text{OH}$ and needs to be explained.

Concept Introduction : In iodoform reaction, the organic compound is added to mixture of iodine and dilutes NaOH. Aldehydes and ketones containing ${\text{CH}}_{\text{3}}\text{C=O}$ give appositive iodoform test by resulting pale yellow precipitate of iodoform.

Answer to Problem 66E

Iodoform test distinguishes between ${\text{CH}}_{\text{3}}{\text{CH}}_{\text{2}}{\text{CH}}_{\text{2}}\text{OH}$ and

Explanation of Solution

Iodoform test distinguishes between alcohol and ketone.

Ketones form yellow precipitate of iodoform in iodoform test.

The reaction is shown below.

  

The alcohols do not undergo iodoform test.

  ${\text{CH}}_{\text{3}}{\text{CH}}_{\text{2}}{\text{CH}}_{\text{2}}{\text{OH+NaOH+I}}_2\to \text{No}\text{reaction}$

(d)

Interpretation Introduction

Interpretation: The test that distinguishes ${\text{CH}}_{\text{3}}{\text{CH}}_{\text{2}}{\text{NH}}_{\text{2}}$ from ${\text{CH}}_{\text{3}}{\text{OCH}}_{\text{3}}$ needs to be explained.

Concept Introduction: In carbylamines reaction, amine is heated with alcoholic KOH and chloroform. If the amine is primary amine, isocyanide (carbylamine) is formed which are bad smelling substances.

Answer to Problem 66E

Carbylamine test distinguishes ${\text{CH}}_{\text{3}}{\text{CH}}_{\text{2}}{\text{NH}}_{\text{2}}$ from ${\text{CH}}_{\text{3}}{\text{OCH}}_{\text{3}}$ .

Explanation of Solution

Amines react with chloroform and a solution of potassium hydroxide (KOH) to produce a bad odour (Carbyamine test) but ether does not undergo this test.

  

But ether does not undergo this reaction.

  ${\text{CH}}_{\text{3}}{\text{OCH}}_{\text{3}}+{\text{CHCl}}_{\text{3}}+3\text{KOH}\to \text{No}\text{reaction}$