Ethers Flashcards
What are ethers
Organic compounds that contain two alkyl groups attached to an oxygen R-O-R
What is the general formula of saturated ethers
CnH2n+2O
How do you name ethers
As alkoxyalkanes.
What are the physical properties of ethers
They are subject only to van der Waals forces but they have permanent dipoles so strong attraction
Why do ethers have higher boiling points than alkanes
They have permanent dipoles so attraction is stronger than in alkanes
Why do ethers have lower boiling points then equivalent alcohols
They can only act as hydrogen bond acceptors. Alcohols can act as hydrogen bond donors and hydrogen bond acceptors
Which ethers give higher boiling points
Larger ethers give higher boiling points
How can ethers be formed
From alcohols or halogenoalkanes
How can ethers be formed from alcohols
By dehydration of alcohols using acid
What is the mechanism of forming ethers from alcohols when one alcohol is present
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.
Why is the acid in the formation of ethers from alcohols catalytic
It is regenerated during the reaction. H+ used in 1st step and produced in 3rd step
What happens is a mixture of alcohols is used to make ethers
It gives 3 products. Two symmetric ethers and an asymmetric ether
What method is used to produce asymmetric ethers
Formation of ethers from alcohols using 2 different types of alcohols
How are ethers formed from halogenoalkanes
By nucleophilic substitution of a halogenoalkane with an alcohol or alkoxide
Describe the mechanism of formation of an ether by nucleophilic substitution of an halogenoalkane with an alcohol
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.
What type of reaction occurs when an ether is formed by nucleophilic substitution of a primary halogenoalkane with an alcohol
Sn2 as the carbon on the electrophile (halogenoalkane) is accessible
What type of reaction occurs when an ether is formed by nucleophilic substitution of a secondary halogenoalkane with an alcohol
Both Sn1 and Sn2
What type of reaction occurs when an ether is formed by nucleophilic substitution of a tertiary halogenoalkane with an alcohol
Sn1 as the carbon on the electrophile (halogenoalkane) is inaccessible but the intermediate carbocation is relatively stable.
Describe the mechanism when ethers are formed by nucleophilic substitution of a halogenoalkane with a alkoxide
Alkoxide (nucleophile) attacks the halogenoalkane (electrophile). Forms an ether and the halogen and spectator anion bond.
Describe the side reactions that occur when ethers are being formed via dehydration of alcohols using an acid
Alcohols can dehydrate directly to alkenes in the presence of acid.
In order for alcohols to dehydrate directly to alkenes what must the acid have
A non-nucleophilic conjugate base to avoid nucleophilic substitution reactions. H2SO4 is a safe bet as sufate is unreactive
What side reactions occur when ethers are formed by nucleophilic substitution of halogenoalkanes with alkoxides
Alkyl halides can also undergo elimination reactions with alkoxides because alkoxides are basic as well as nucleophilic
Describe the mechanism of alkyl halides undergoing an elimination reaction with alkoxides
CH3O- (nucleophile, acting as a base) attacks tertiary halogenoalkane (electrophile). Forms methanol, propane and NaBr (spectator ion and halogen). Reacts by E2
Why is alkyl halides undergoing elimination reactions with alkoxides E2
The rate depends on both the concentration of the alkoxide and halogenoalkane and the reaction proceeds in one step.
What is E2
Bimolecular elimination. The rate depends on the concentrations of both reactants and the reaction proceeds in one step
What is E1
Unimolecular elimination e.g. dehydration of alcohol. Bromide leave first thwn carbocation is deprotonated
Describe reactions of ethers
Ethers are very unreactive and are generally chemically inert
Which types of ethers are an exception to the reactivity behaviour of ethers
Oxiranes (epoxides)
Why are oxiranes an exception
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
