8. Aldehydes and Ketones

Question 1

What is the carbonyl group?

Answer 1

C double bonded to O

Question 2

How are aldehydes named?

Answer 2

Using the suffix -al

Question 3

How are ketones named?

Answer 3

Using the suffix -one, or the prefix oxo-

Question 4

What is a primary alcohol oxidised to?

Answer 4

Aldehyde → Carboxylic acid

Question 5

What is a secondary alcohol oxidised to?

Answer 5

Ketone

Question 6

What would a suitable oxidising agent for primary and secondary alcohols be?

Answer 6

Acidified potassium dichromate

Question 7

Why can ketones not be oxidised?

Answer 7

There is no hydrogen bonded to the carbonyl group

Question 8

What is Fehling’s solution?

Answer 8

An alkaline solution that contains copper ions, which act as a mild oxidising agent

Question 9

What happens when Fehling’s solution is mixed with an aldehyde and heated?

Answer 9

The aldehyde is oxidised to a carboxylic acid and the blue copper (II) ions are reduced to copper (I) oxide as a brick red precipitate

Question 10

What is Tollen’s reagent made of?

Answer 10

Aqueous solutions of ammonia and silver nitrate

Question 11

What happens when Tollen’s reagent is mixed with an aldehyde?

Answer 11

The aldehyde is oxidised to a carboxylic acid and the silver (I) ions are reduced to metallic silver

Question 12

How can the oxidation process that produces aldehydes and ketones be reversed?

Answer 12

With a strong reducing agent (e.g. sodium tetrahydridoborate or lithium aluminium hydride)

Question 13

What reducing agents can be used to reduce aldehydes and ketones?

Answer 13

• sodium tetrahydridoborate - NaBH4 (dissolved in water)

* lithium aluminium hydride (LiAlH4) - (dissolved in a non-aqueous solvent such as ethanol)

Question 14

What do the reducing agents NaBH4 and LiAlH4 provide?

Answer 14

The hydride ion (H+) which acts as a nucleophile

Question 15

In the reduction of aldehydes and ketones, what does the hydride ion from the reducing agent act as?

Answer 15

A nucleophile

Question 16

What is formed when carboxylic acids are reduced?

Answer 16

Aldehyde → Primary Alcohol

Question 17

What is formed when ketones are reduced?

Answer 17

Secondary alcohols

Question 18

What type of mechanism is the reduction of an aldehyde?

Answer 18

Nucleophilic addition

Question 19

What type of mechanism is the reduction of a ketone?

Answer 19

Nucleophilic addition

Question 20

What does the addition of cyanide to an aldehyde or ketone form?

Answer 20

A hydroxynitrile

Question 21

What kind of mechanism is it when cyanide and an aldehyde/ketone forms a hydroxynitrile?

Answer 21

Nucleophilic addition

Question 22

What is the reagent when a hydroxynitrile is formed from an aldehyde/ketone?

Answer 22

KCN or NaCN (followed by H2SO4)

Question 23

What is the nucleophile when a hydroxynitrile is formed from an aldehyde/ketone?

Answer 23

:CN-

Question 24

Can hydroxynitrile be formed from aldehydes/ketones in a lab?

Answer 24

No

Question 25

Why can't hydroxynitrile be formed from aldehydes/ketones in a lab?

Answer 25

HCN is a very toxic gas and high flammable

Question 26

How is HCN stored?

Answer 26

It is not stored, by made in situ by mixing KCN and dilute acid

Question 27

What are the equations to show how HCN is produced in situ?

Answer 27

* sulphuric acid: 2KCN(s) + H2SO4 → 2HCN(g) + K2SO4 | * hydrochloric acid: KCN(s) + HCl → HCN(g) + KCl

Question 28

If HCN is stored, what is the best way to store it?

Answer 28

As a solid

Question 29

Is HCN toxic?

Answer 29

Yes

Question 30

In the formation of hydroxynitrile from aldehydes/ketones, when will chiral molecules be formed?

Answer 30

When the reactants are aldehydes or unsymmetrical ketones

Question 31

Can the products of the reactions of cyanide with aldehyde/ketones display optical isomerism?

Answer 31

Yes - if the reactant is an aldehyde or an unsymmetrical ketone

Question 32

Why do the products aldehydes and unsymmetrical ketones with HCN display optical isomerism?

Answer 32

The carbonyl group is planar meaning there is an equal chance that the nucleophile will attack either side of the molecule resulting in a racemate

Question 33

Conditions of oxidation of an aldehyde to carboxylic acid?

Answer 33

Warm under reflux

Question 34

Observation for oxidation of an aldehyde to carboxylic acid?

Answer 34

Orange to green

Question 35

Conditions for reduction of carbonyl to alcohol?

Answer 35

Room temperature

Question 36

Conditions for addition of HCN carbonyl to hydroxynitrile?

Answer 36

Room temperature