Chapter 16, Problem 78P

Interpretation Introduction

(a)

Interpretation:

The products should be identified by the reaction of 2,6-dimethyl-3-heptanone with $H_2,Pd$.

Concept Introduction:

Addition of H₂gas to a multiple bond is known as hydrogenation. In the presence of palladium metal as the catalyst, H₂ molecules react with ketones and give the respective secondary alcohol of the particular ketone.

Answer to Problem 78P

Explanation of Solution

When a ketone reacts with H₂ gas in the presence of palladium metal resulting product is the secondary alcohol of the initial ketone molecule. Palladium metal act as a catalyst to the reaction that provides a surface to bind both the H₂ and carbonyl compound which reduce the activation energy of the reaction.

Hydrogen atoms in the alcohol molecule shown below, which are indicated in red color are the added H during the hydrogenation reaction.

Interpretation Introduction

(b)

Interpretation:

The products should be identified by the reaction of 2,6-dimethyl-3-heptanone with $K_{2}C{r}_2{O}_7$.

Concept Introduction:

Addition of an O atom in to a molecule is known as oxidation. If a carbonyl atom consists of a hydrogen atom directly connected to the carbonyl C, it will be oxidized in the presence of an oxidizing agent such as $K_{2}C{r}_2{O}_7$ and give the respective carboxylic acid. But ketones do not contain any hydrogen atom bonded to the carbonyl group, they are not going oxidize to a carboxylic acid.

Answer to Problem 78P

No reaction.

Explanation of Solution

Addition of an O atom in to a molecule is known as oxidation. If a carbonyl atom consists of a hydrogen atom directly connected to the carbonyl C, it will be oxidized in the presence of an oxidizing agent such as $K_{2}C{r}_2{O}_7$ and give the respective carboxylic acid. But ketones do not contain any hydrogen atom bonded to the carbonyl group, they are not going oxidize to a carboxylic acid. So, there is no reaction of ketones with $K_{2}C{r}_2{O}_7$.

Hence, during the reaction no color change can be observed.

Interpretation Introduction

(c)

Interpretation:

The products should be identified by the reaction of 2,6-dimethyl-3-heptanone with $A{g}_{2}O,N{H}_{4}OH$.

Concept Introduction:

Addition of an O atom in to a molecule is known as oxidation. If a carbonyl atom consists of a hydrogen atom directly connected to the carbonyl C, it will be oxidized in the presence of an oxidizing agent such as ( $A{g}_{2}O$ ) in an aqueous medium of ammonium hydroxide ( $N{H}_{4}OH$ ) and give the respective carboxylic acid. But ketones do not contain any hydrogen atom bonded to the carbonyl group, they are not going oxidize to a carboxylic acid.

Answer to Problem 78P

No reaction.

Explanation of Solution

Addition of an O atom in to a molecule is known as oxidation. If a carbonyl atom consists of a hydrogen atom directly connected to the carbonyl C in an it will be oxidized in the presence of an oxidizing agent such as $A{g}_{2}O$ in an aqueous medium of ammonium hydroxide( $N{H}_{4}OH$ ), (this $A{g}_{2}O,N{H}_{4}OH$ known as as Tollens reagent)and give the respective carboxylic acid. But ketones do not contain any hydrogen atom bonded to the carbonyl group, they are not going oxidize to a carboxylic acid. So, there is no reaction of ketones with $A{g}_{2}O,N{H}_{4}OH$.

Hence, during the reaction is no silver mirror can be observed.

Interpretation Introduction

(d)

Interpretation:

The products should be identified by the reaction of 2,6-dimethyl-3-heptanone with $C{H}_{3}OH(2\text{ equivalents), }{H}_2{\text{SO}}_4$.

Concept Introduction:

In the presence of alcohol in the acidic medium, ketones undergo addition reactions and give acetal in two steps.

Hydrogen atom and CH₃ groups in the acetal and hemiacetal molecules shown below, which are indicated in red color are the added molecules during the reaction.

Answer to Problem 78P

Explanation of Solution

In the presence of alcohol in the acidic medium, ketones undergo addition reactions and give acetal in two steps. In the first step ketones form hemiacetals and during the second step it converts to an acetal molecule of the respective ketone molecule.

Addition of one molecule of alcohol in to a ketone forms a hemiacetal, one bond of the $C=O$ is broken and two new single bonds are formed. In the presence of $C{H}_{3}OH\text{, }{H}_2{\text{SO}}_4$ , acyclic hemiacetals react with another alcohol molecule and produce acetals due to the un stability of the acyclic hemiacetal molecule.

Hydrogen atom, CH₃ and OCH₃ groups in the acetal and hemiacetal molecules shown below, which are indicated in red color are the added molecules during the reaction.

Interpretation Introduction

(e)

Interpretation:

The products should be identified by the reaction of 2,6-dimethyl-3-heptanone with $C{H}_{3}C{H}_{2}OH(2\text{ equivalents), }{H}_2{\text{SO}}_4$.

Concept Introduction:

In the presence of alcohol in the acidic medium, aldehydes undergo addition reactions and give acetal in two steps.

Hydrogen atom and CH₂CH₃ groups in the acetal and hemiacetal molecules shown below, which are indicated in red color are the added molecules during the reaction.

Answer to Problem 78P

Explanation of Solution

In the presence of alcohol in the acidic medium, ketones undergo addition reactions and give acetal in two steps. In the first step ketones form hemiacetals and during the second step it converts to an acetal molecule of the respective ketone molecule.

Addition of one molecule of alcohol in to aketone forms a hemiacetal, one bond of the $C=O$ is broken and two new single bonds are formed. In the presence of $C{H}_{3}C{H}_{2}OH\text{, }{H}_2{\text{SO}}_4$ , acyclic hemiacetals react with another alcohol molecule and produce acetals due to the un stability of the acyclic hemiacetal molecule.

Hydrogen atom, CH₂CH₃ and OCH₂CH₃ groups in the acetal and hemiacetal molecules shown below, which are indicated in red color are the added molecules during the reaction.

Interpretation Introduction

(f)

Interpretation:

The products should be identified by the reaction of ${(C{H}_3)}_{2}CHC{(OC{H}_{2}C{H}_3)}_2{(C{H}_2)}_{2}CH{(C{H}_3)}_2$ with ${\text{H}}_2\text{O, }{H}_2{\text{SO}}_4$.

Concept Introduction:

In the presence of water and acid, acetals undergo hydrolysis reaction and produce aldehydes.

OR' groups in the acetal molecule shown below, which are indicated in red color are the molecules which becomes alcohol molecules during the hydrolysis.

Answer to Problem 78P

Explanation of Solution

Acetals are stable molecules, but their bonds can cleave by a reaction with water and produce aldehydes.

In the acetal molecule, two bonds of the $C-O$ are broken and $C=O$ formed, each CH₂CH₃ group becomes a molecule of alcohol.

CH₂CH₃ groups in the acetal molecule shown below, which are indicated in red color are the molecules which becomes alcohol molecules during the hydrolysis.