Chapter 15, Problem 15.111EP

(a)

Interpretation Introduction

Interpretation:

Condensed structural formula of the organic product that is formed when pentanal is treated with hydrogen in presence of nickel catalyst has to be given.

Concept Introduction:

In organic chemistry, oxidation reaction is referred to the number $\text{C}-\text{O}$ bonds increase and/or number of $\text{C}-\text{H}$ bonds decrease.

In organic chemistry, reduction reaction is referred to the number $\text{C}-\text{O}$ bonds decrease and/or number of $\text{C}-\text{H}$ bonds increase.

Alcohols undergo oxidation reaction and reduction reaction.  This depends upon the number of hydrogen atoms that is bonded to the alpha carbon atom.  Primary and secondary alcohol undergoes oxidation reaction while tertiary alcohol does not undergo oxidation reaction.  Primary alcohols undergo oxidation to give aldehyde and carboxylic acid as product.  Secondary alcohol undergoes oxidation to give ketone as the product.

Aldehyde undergoes oxidation to give carboxylic acid as the product while ketone does not undergo oxidation reaction.

The reverse of oxidation reaction is reduction reaction.  Reduction of aldehyde gives primary alcohol as the product and reduction of ketone gives secondary alcohol as the product.  Reduction can be accomplished using hydrogen gas and a metal catalyst namely nickel.

(b)

Interpretation Introduction

Interpretation:

Condensed structural formula of the organic product that is formed when pentanal is treated with ethanol in 1 to 1 reacting ratio has to be given.

Concept Introduction:

Aldehydes contain a carbonyl group that is bonded to a hydrogen atom and a carbon atom.  Ketones are compounds that contain a carbonyl group bonded to two carbon atoms.  Aldehydes and ketones undergo addition reaction across the carbonyl group.

Aldehydes and ketones react with alcohol to form hemiacetal as the product.  This reacts with further molecule of aldehyde or ketone to form acetal.

Hemiacetal is an addition product that is obtained by reaction between aldehyde or ketone with alcohol.  The general reaction of hemiacetal formation can be given as,

(c)

Interpretation Introduction

Interpretation:

Condensed structural formula of the organic product that is formed when pentanal is treated with methanol in 1 to 2 reacting ratio has to be given.

Concept Introduction:

Aldehydes contain a carbonyl group that is bonded to a hydrogen atom and a carbon atom.  Ketones are compounds that contain a carbonyl group bonded to two carbon atoms.  Aldehydes and ketones undergo addition reaction across the carbonyl group.

Aldehydes and ketones react with alcohol to form hemiacetal as the product.  This reacts with further molecule of aldehyde or ketone to form acetal.

Hemiacetal is an addition product that is obtained by reaction between aldehyde or ketone with alcohol.  The general reaction of hemiacetal formation can be given as,

From the above general structure of hemiacetal it is found that it is an organic compound that contains a carbon atom that is bonded to an alkoxy group and a hydroxyl group.

Acetal is formed when the formed hemiacetal reacts with further alcohol molecule so that the hydroxyl group in the hemiacetal is converted into alkoxy group.  This can be shown as given below,

The alcohol that is reacting with the hemiacetal can be from the same alcohol which involved in formation of hemiacetal or a different alcohol molecule.  Therefore, the ketone or aldehyde must react with two alcohol molecules that may or may not be identical to form acetal.

(d)

Interpretation Introduction

Interpretation:

Condensed structural formula of the organic product that is formed when pentanal is treated with ${\text{K}}_{\text{2}}{\text{Cr}}_{\text{2}}{\text{O}}_{\text{7}}$ has to be given.

Concept Introduction:

In organic chemistry, oxidation reaction is referred to the number $\text{C}-\text{O}$ bonds increase and/or number of $\text{C}-\text{H}$ bonds decrease.

In organic chemistry, reduction reaction is referred to the number $\text{C}-\text{O}$ bonds decrease and/or number of $\text{C}-\text{H}$ bonds increase.

Alcohols undergo oxidation reaction and reduction reaction.  This depends upon the number of hydrogen atoms that is bonded to the alpha carbon atom.  Primary and secondary alcohol undergoes oxidation reaction while tertiary alcohol does not undergo oxidation reaction.  Primary alcohols undergo oxidation to give aldehyde and carboxylic acid as product.  Secondary alcohol undergoes oxidation to give ketone as the product.

Aldehyde undergoes oxidation to give carboxylic acid as the product while ketone does not undergo oxidation reaction.