Ethers Flashcards
What are ethers?
2
A class of organic compounds containing an O atom bonded by a single bond to two alkyl and or aryl groups
The two alkyl/aryl groups can be the same or different
What is the O in ethers bonded to?
To two alkyl and/or aryl groups
What type of bond is found between the O and the alkyl/aryl groups in ethers?
A single group
What is an alkyl group?
Its an alkane with a hydrogen atom missing from its chain
What is the general formula of an alkyl group?:
Cn H(2n+1)
What is the smallest alkyl group?
The methyl group (CH3)
What is an aryl group?
A simple aromatic compound with one of its hydrogen atoms missing (this missing atom allows the molecule to attach to a carbon chain)
Give an example of an aryl group.
Tolyl group (derived from toluene - a benzene ring with the substitution of a methyl group)
How are ethers named if both of their groups are alkyl groups?
The ether is usually named as alkyl aklyl ether
The alkyl groups are listed in alphabetical order
If the two alkyl groups are the same then it’s a dialkyl ether
Give an example of a dialkyl ether.
Dimethyl ether (an O singly bonded to two methyl groups - CH3)
When naming an ether with two alkyl groups, how do you decide the order of naming the alkyl groups?
The alkyl groups are listed in alphabetical order
How do you name an ether which has two of the same alkyl groups?
Dialkyl ether
How is an ethyl group written in an ether?
CH3 CH2
How do you go about naming intermediate ethers?
You treat the ether group as an alkoxy group
The root name is defined by the more complex group i.e. longer chain
What is the formula for methoxy?
CH3O
What is the name given to CH3CH2O?
Ethoxy
What exactly is an intermediate ether?
An ether where there is one complex group
What exactly is a complex ether?
An ether where there is two complex group
How do you name a complex ether?
Ether is treated as a chain substituent and given the prefix oxa
What three factors affect boiling point?
3
Relative strength of intermolecular forces; coulombic forces > dipole forces > induced dipole forces
B.p increases with increasing molecular mass i.e. number of C atoms and FGs present
Molecular symmetry or lack thereof - b.p. decreases with branching
List the intermolecular forces in order of increasing strength.
Ionic > H-bonding > Dipole-dipole > induced dipole - induced dipole
What is the relationship between a compound’s molar mass and boiling point?
Boiling point increases with molecular mass i.e. the number of C atoms anf FGs present
What is the relationship between molecular symmetry and boiling point?
Boiling point decreases with branching
Symmetrical molecules with no branching have higher boiling points
How do the boiling points of ethers compare to that of alcohols with an equal number of C atoms?
Ethers have lower boiling points than these alcohols
When will ethers undergo H-bonding?
The O of ethers will undergo H-bonding with H2O
Are ethers soluble in water?
Only some ethers are soluble in water
Which ethers are soluble in water?
Ethers that contain up to 3 carbon atoms due to their H-bond formation with water molecules
What state are ethers in at room temperature?
2
Most are colourless volatile liquids with pleasant ether smells
Dimethylether and ethyl methyl ether are gases at ordinary temperature
Describe the density of ethers.
Ethers are less dense than water -> float on water
Describe the flammability of ethers.
Ethers are highly flammable - must not be used in presence of flame
How are ethers synthesized?
By reacting alkyl halides (or other substrates which are good leaving groups) with an alkoxide ion in a substitution reaction
What is an alkyl halide?
2
Haloalkanes
Alkane with one or more halogen
What is an alkoxide ion?
The conjugated base (deprotonated form) of an alcohol
Are alcohols nucleophiles or electrophiles?
Alcohols are weak nucleophiles
Since alcohols are weak nucleophiles, what does this make alkoxide ions?
This makes them good nucleophiles
Explain in your own words the substitution reaction that needs to take place to synthesise an ether.
A deprotonated alcohol is reacted with a haloalkane to form an ether
What type of alkyl halide doesn’t work well to form an ether?
Secondary alkyl halides don’t work well
How can the synthesis of an ether using a secondary alkyl halide reaction be improved?
A polar aprotic solvent such as dimethyl-sulphoxide (DMSO) can be used
What type of alkyl halide cannot be used to form ethers?
Tertiary alkyl halides even with DMSO
What can readily be given from an elimination reaction using a tertiary alkyl halide?
An alkene can be formed
How are alkoxide ions formed from alcohols?
The alcohol is deprotonated by using a super strong base such as sodium hydride
Why are ethers widely used as solvents?
Ethers are inert - very unreactive
Most ethers are inert, what ethers are exceptions to this statement?
Epoxides
What are epoxides?
Ethers that are highly reactive due to ring strain
What is cleavage of a molecule?
The splitting of chemical bonds
What is required for cleavage of ethers?
Harsh conditions e.g. strong acids
What are the two steps in ether cleavage?
Protonation by a strong acid to generate a good leaving group
Then a substitution reaction by a decent nucleophile
What happens when an ether is exposed to the air for a long time?
The ether may contain organic peroxides due to air oxidation which can be a safety hazard as they are explosive
How are peroxides detected in ethers?
Using a dip-stick
How are peroxides removed from ethers?
By shaking with aqueous ferrous sulfate (FeSO4)
