Ethers

Question 1

What are ethers

Answer 1

Organic compounds that contain two alkyl groups attached to an oxygen R-O-R

Question 2

What is the general formula of saturated ethers

Answer 2

CnH2n+2O

Question 3

How do you name ethers

Answer 3

As alkoxyalkanes.

Question 4

What are the physical properties of ethers

Answer 4

They are subject only to van der Waals forces but they have permanent dipoles so strong attraction

Question 5

Why do ethers have higher boiling points than alkanes

Answer 5

They have permanent dipoles so attraction is stronger than in alkanes

Question 6

Why do ethers have lower boiling points then equivalent alcohols

Answer 6

They can only act as hydrogen bond acceptors. Alcohols can act as hydrogen bond donors and hydrogen bond acceptors

Question 7

Which ethers give higher boiling points

Answer 7

Larger ethers give higher boiling points

Question 8

How can ethers be formed

Answer 8

From alcohols or halogenoalkanes

Question 9

How can ethers be formed from alcohols

Answer 9

By dehydration of alcohols using acid

Question 10

What is the mechanism of forming ethers from alcohols when one alcohol is present

Answer 10

With ethanol: Oxygen of hydroxyl group acts as nucleophile and attacks electrophile so alcohol becomes protonated (fast). Protonated alcohol is then attacked by alcohol (nucleophile) by SN2 and water is produced. Then intermediate loses a H+ ion from the centre of the ether and an ether is formed.

Question 11

Why is the acid in the formation of ethers from alcohols catalytic

Answer 11

It is regenerated during the reaction. H+ used in 1st step and produced in 3rd step

Question 12

What happens is a mixture of alcohols is used to make ethers

Answer 12

It gives 3 products. Two symmetric ethers and an asymmetric ether

Question 13

What method is used to produce asymmetric ethers

Answer 13

Formation of ethers from alcohols using 2 different types of alcohols

Question 14

How are ethers formed from halogenoalkanes

Answer 14

By nucleophilic substitution of a halogenoalkane with an alcohol or alkoxide

Question 15

Describe the mechanism of formation of an ether by nucleophilic substitution of an halogenoalkane with an alcohol

Answer 15

Alcohol (nucleophile) attacks a halogenoalkane (electrophile). Forms an ether with H still attached to oxygen and halogen is released. Halogen and hydrogen bond and an ether is formed.

Question 16

What type of reaction occurs when an ether is formed by nucleophilic substitution of a primary halogenoalkane with an alcohol

Answer 16

Sn2 as the carbon on the electrophile (halogenoalkane) is accessible

Question 17

What type of reaction occurs when an ether is formed by nucleophilic substitution of a secondary halogenoalkane with an alcohol

Answer 17

Both Sn1 and Sn2

Question 18

What type of reaction occurs when an ether is formed by nucleophilic substitution of a tertiary halogenoalkane with an alcohol

Answer 18

Sn1 as the carbon on the electrophile (halogenoalkane) is inaccessible but the intermediate carbocation is relatively stable.

Question 19

Describe the mechanism when ethers are formed by nucleophilic substitution of a halogenoalkane with a alkoxide

Answer 19

Alkoxide (nucleophile) attacks the halogenoalkane (electrophile). Forms an ether and the halogen and spectator anion bond.

Question 20

Describe the side reactions that occur when ethers are being formed via dehydration of alcohols using an acid

Answer 20

Alcohols can dehydrate directly to alkenes in the presence of acid.

Question 21

In order for alcohols to dehydrate directly to alkenes what must the acid have

Answer 21

A non-nucleophilic conjugate base to avoid nucleophilic substitution reactions. H2SO4 is a safe bet as sufate is unreactive

Question 22

What side reactions occur when ethers are formed by nucleophilic substitution of halogenoalkanes with alkoxides

Answer 22

Alkyl halides can also undergo elimination reactions with alkoxides because alkoxides are basic as well as nucleophilic

Question 23

Describe the mechanism of alkyl halides undergoing an elimination reaction with alkoxides

Answer 23

CH3O- (nucleophile, acting as a base) attacks tertiary halogenoalkane (electrophile). Forms methanol, propane and NaBr (spectator ion and halogen). Reacts by E2

Question 24

Why is alkyl halides undergoing elimination reactions with alkoxides E2

Answer 24

The rate depends on both the concentration of the alkoxide and halogenoalkane and the reaction proceeds in one step.

Question 25

What is E2

Answer 25

Bimolecular elimination. The rate depends on the concentrations of both reactants and the reaction proceeds in one step

Question 26

What is E1

Answer 26

Unimolecular elimination e.g. dehydration of alcohol. Bromide leave first thwn carbocation is deprotonated

Question 27

Describe reactions of ethers

Answer 27

Ethers are very unreactive and are generally chemically inert

Question 28

Which types of ethers are an exception to the reactivity behaviour of ethers

Answer 28

Oxiranes (epoxides)

Question 29

Why are oxiranes an exception

Answer 29

Ring strain. Oxiranes are strongly electrophilic and very reactive necause their bond angles are 60 degrees instead of the desired 109 degrees. This creates strain making them unstable. Opening the ring by nucleophilic attack relieves this strain and so is a very easy reaction