Elimination reactions
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What is an elimination reaction?
the loss of a leaving group and the formation of an alkene
What does the nucleophile act as in an elimination reaction?
base
How many molecules are involved in the rate determining step in E1?
1
Why is HSO4- a poor nucleophile?
It is a very weak base It is stable as the negative charge is spread across the 3 atoms
Which step is the rate determining step in E1?
The slow step the kicking out of the leaving group
How is the carbenium ion stabilised in E1?
Sigma conjugation electron density is donated from the C-H bond which breaks to the carbenium ion
Why is a tertiary carbenium ion the most stable?
There are 3 lots of sigma conjugation which means it is more stable
What is an intramolecular electron source?
The C-H bond which is adjacent to the carbenium io
Why does an intramolecular substitution just happen (E1) ?
It wants to lower the energy of the system as it has a positive charge
How many molecules are involved in the rate determining step for E2?
2
Why is the nucleophile acting as a base?
It is attacking the hydrogen and not the carbon
What are the steps of an E1 reaction?
Leaving group is protonated to make it a better leaving group L.G kicked out leaving a carbenium ion Nucleophile attacks the carbenium ion
For E1 reactions, what is the order of reactivity related to?
Stability of the intermediate carbenium ion The more stable, the better the E1 will be
When is elimination not possible?
When there are no hydrogens β-to the leaving group
What type of solvents favour E1 reactions and why?
Polar They can stabilise the charged, ionic intermediate
What is the issue with using H2O as a solvent?
It is too polar, organic molecules don’t dissolve
What are some examples are polar solvents?
ROH DMSO DMF
What are some examples of mid-polar solvents?
THF Et2O DCM EtOAc
What are some examples of non-polar solvents?
Hexane Petrol Toulene Benzene
How does the leaving group influence the rate of reaction?
It is involved in the rate determining step so the better the leaving group the faster the reaction
Why is the E1 reaction for primary or secondary alcohols slow?
The secondary carbenium ion is not stable
Why would an E2 reaction for primary or secondary alcohols not happen?
A strong base would deprotonate the OH rather than the hydrogen adjacent to the OH group
The stronger the base…
The more likely it is to take only the most acidic hydrogen
What is alcohol activation?
Converting OH into a better leaving group which is usually done through the formation of a tosylate