Ethers and Epoxides. Flashcards
What is the bond angle of water?
105 Degrees.
What is the bond angle of methanol?
108.5 Degrees.
What is the bond angle of dimethyl ether?
112 Degrees.
What is the bond angle of di tert butyl ether?
132 Degrees.
Are the boiling points of ethers closer to alkanes or alcohols?
The boiling points of ethers are closer to alkanes than alcohols.
What are the major contributors in the bonds of ethers, dipole dipole or dispersion forces?
The dipole-dipole attractive forces are minor contributors. The dispersion forces are the major contributors to intermolecular attractions.
Do ethers have hydrogen bonding?
Ethers do not have OH groups hence the reason for the lack of hydrogen bonding.
What is an ether?
R-O-R.
Are ethers soluble in water?
Yes.
When a Grignard reagent reacts with ethylene oxide, what is produced?
A primary alcohol.
Epoxide + LiAlH4 gives what?
An alcohol.
When a Grignard reagent reacts with ethylene oxide the attack takes place on which carbon?
The less substituted carbon.
Are ethers symmetrical or unsymmetrical?
They can be both.
What molecular geometry do ethers have?
Bent.
The oxygen on an ether has what hybridisation?
SP3.
What is a heterocyclic ether?
The oxygen is part of the ring.
What is the Williamson Ether synthesis?
This method involves an SN2 attack of the alkoxide on an unhindered primary halide or tosylate.
What is a alkoxymercuration–Demercuration Reaction?
Use mercuric acetate with an alcohol. The alcohol will react with the intermediate mercurinium ion by attacking the more substituted carbon.
Why are ethers good solvents?
Ethers are unreactive, which makes them ideal solvents for a lot of different reactions.
How can ethers be cleaved?
They can be cleaved by heating with HBr and HI.
What is more reactive, HI or HBr?
HI.
How does a phenyl ether cleavage work?
An alcohol is formed on the phenyl group as Phenol cannot react further to become halide because an SN2 reaction cannot occur on an sp2 carbon.
What are sulfides?
R-S-R.
How are thiolates synthesised?
Thiolates are easily synthesized by the Williamson ether synthesis, using dithiolate as the nucleophile.
How are epoxides synthesised?
Peroxyacids are used to convert alkenes to epoxides. Most commonly used peroxyacid is meta-chloroperoxybenzoic acid (MCPBA).
The reaction is carried out in an aprotic acid to prevent the opening of the epoxide.
How will ethers enable unstable molecules to be used as reagents?
Ethers will often form complexes with molecules that have vacant orbitals, enabling ‘unstable’ molecules to be used as reagents.
What are crown ethers?
Crown ethers are macrocyclic ethers, which help to solvate metal cations, and thus allow inorganic salts to dissolve in organic solvents.
What are oxetanes?
These are four membered rings with one oxygen.
What are furans?
These are five membered rings with one oxygen and two double bonds.
What are pyrans?
These are six membered rings with one oxygen and two double bonds.
What are dioxanes?
These are six membered rings with two oxygens.
What are the 2 types of reactions that ethers can undergo?
Cleavage and oxidation.
Ether cleavage produces what?
An alcohol and an alkyl halide.
Phenyl ethers cleave to give what?
Alkyl halides and phenols.
Why does the reaction stop at the phenol stage?
The reaction stops at the phenol stage since the sp2 carbon of the C-OH bond does not allow the required SN1 or SN2 reactions to generate the second molecule of aryl halide.
What is one of the most common epoxidising reagents?
MCPBA
What reagents will attack ethers and epoxides?
Grignard and organolithium reagents also attack epoxides at the least hindered carbon to generate alcohols.
