Carbonyl Compounds

Question 1

What is

the carbonyl group?

Answer 1

C=O

Question 2

What are

carbonyl compounds?

Answer 2

Organic compounds that have the carbonyl group

Question 3

What two homologous series are considered

when talking about carbonyl compounds?

Answer 3

Aldehydes & Ketones

Question 4

What is another name for

an Aldehyde?

Answer 4

an Alkanal

Question 5

What is another name for

a Ketone?

Answer 5

an Alkanone

Question 6

What is the general formula for an aldehyde?

Answer 6

RCOH

Question 7

What is the general formula for a ketone?

Answer 7

RCOR’

Question 8

What is more reactive: an aldehyde or a ketone?

Answer 8

An aldehyde

Question 9

What reactions do carbonyl compounds typically undergo?

Answer 9

Nucleophilic addition reactions

the nucleophiles are attracted to the electron-rich C=O

Question 10

Why do carbonyl compounds undergo nucleophilic addition reactions?

Answer 10

The carbon in the C=O bond has a partially positive charge due to the electronegativity difference between carbon and oxygen

Therefore the carbon there is an electrophile (e^- deficient specie)

Question 11

Can aldehydes be oxidised?

Answer 11

Yes. They oxidise to carboxylic acids

Question 12

Can ketones be oxidised?

Answer 12

No

Question 13

Why can’t ketones be oxidised?

Answer 13

Oxidation is also the removal of hydrogen, in the ketone structure, RCOR, there is no hydrogen directly bonded to the carbon atom to be removed

Question 14

Can aldehydes be reduced?

Answer 14

Yes. They are reduced to PRIMARY alcohols

Question 15

Can ketones be reduced?

Answer 15

Yes. They are reduced to SECONDARY alcohols

Question 16

How are aldehydes produced?

Answer 16

The oxidation of primary alcohols

Question 17

What are reaction conditions for the production of aldehydes by the oxidation of primary alcohols

Answer 17

1. Distillation
2. Heating of the reacting system
3. Acidified K₂Cr₂O₇ / Acidified KMnO₄

Question 18

In what other way

can aldehydes be produced?

Answer 18

The (incomplete) reduction of carboxylic acids

Question 19

How are ketones produced?

Answer 19

The oxidation of secondary alcohols

Question 20

What are reaction conditions for the production of ketones by the oxidation of secondary alcohols

Answer 20

1. Heating of the reacting system
2. Acidified K₂Cr₂O₇ / Acidified KMnO₄

Question 21

What are both aldehydes and ketones reduced to?

Answer 21

Alcohols

Question 22

Name the nucleophile

that can reduce aldehydes and ketones to alcohols

Answer 22

The hydronium ion (H^-)

Question 23

Name the 2 nucleophiles

that can reduce aldehydes and ketones reduced to alcohols

Answer 23

1. The water molecule
2. The hydroxide group

Question 24

What type of isomerism

relates an aldehyde to its corresponding ketone

(by that I mean they have the same number of carbons)

Answer 24

Structural Isomerism

Specifically functional group isomerism

Question 25

# What is a **symmetric** ketone?

Answer 25

A ketone with **the same number of carbons** on either side of the carbonyl group ## Footnote Eg: Propanone

Question 26

# What is an **asymmetric** ketone?

Answer 26

A ketone with **an unequal number of carbons** on either side of the carbonyl group

Question 27

Can aldehydes be symmetric or asymmetric?

Answer 27

**No**

Question 28

Why can't aldehydes be symmetric or asymmetric?

Answer 28

Because they are formed from primary alcohols that have only one other alkyl group attached to them. The carbonyl group is **always on the terminal carbon**

Question 29

# What result is expected in the reaction of carbonyl compounds with 2,4-dinitrophenylhydrazine?

Answer 29

There will be a red-orange precipitate

Question 30

# Do **carboxylic acids** produce any precipitate with 2,4-dinitrophenylhydrazine?

Answer 30

**No**

Question 31

# What is the limitation of the reaction of carbonyl compounds with 2,4-dinitrophenylhydrazine?

Answer 31

It does not differentiate between aldehydes and ketones, **it just shows the presence of the carbonyl group**

Question 32

# What type of reaction is the reaction of carbonyl compounds with 2,4-dinitrophenylhydrazine?

Answer 32

**A *condensation* reaction** ## Footnote A molecule of water is eliminated

Question 33

# How can we differentiate between aldehydes and ketones?

Answer 33

Using the Tollen's test

Question 34

# What is observed when aldehydes react with Tollen's reagent?

Answer 34

A silver precipitate is formed on the walls of the test tube ## Footnote Tollen's reagent contains silver ions which are **reduced to metallic silver** when they react with the aldehyde.

Question 35

# What is observed when ketones react with Tollen's reagent?

Answer 35

**Nothing** ## Footnote Ketons **do not react** with Tollen's reagent.

Question 36

# What difference between aldehydes and ketones is *typically exploited* when using the Tollen's test?

Answer 36

Aldehydes are readily oxidised and ketones are not, hence, they do not react with Tollen's reagent

Question 37

# What other solution can you use to distinguish between aldehydes and ketones besides Tollen's reagent?

Answer 37

Fehling's solution

Question 38

# What is observed when ketones react with Fehling's solution?

Answer 38

**Nothing** ## Footnote Ketones **do not reduce** Fehling's solution, so the blue coloured Cu²⁺ ions remain

Question 39

# What is observed when aldehydes react with Fehling's solution?

Answer 39

The solution turns from blue to (brick) red ## Footnote Fehling's solution contains Cu²⁺ ions which are **reduced to Cu⁺ ions ** when they react with the aldehyde. Copper (I) is brown in colour

Question 40

# What is observed when ketones react with Acidified potassium dichromate?

Answer 40

**No visible change**

Question 41

# What is observed when aldehydes react with Acidified potassium dichromate?

Answer 41

The solution turns from orange to green ## Footnote Acidified potassium dichromate is an **oxidising agent**; oxidising the aldehyde to an alkanoic acid and getting reduced from Cr⁶⁺ to Cr³⁺ in the process.

Question 42

# What is the precipitates when aldehydes react with Fehling's solution?

Answer 42

Copper (I) oxide (Cu₂O)

Question 43

# What are the reaction conditions for an aldehyde to react with Fehling's solution?

Answer 43

The solution must be **warmed**

Question 44

# What are the reaction conditions for an aldehyde to react with Acidified potassium dichromate?

Answer 44

The reacting system must be **warmed**