Halogenoalkanes Nucleophilic Elimination Flashcards
What is elimination
The removal of a small molecule and the formation of a carbon carbon double bond
Conditions for elimination
Add potassium hydroxide in ethanol with no water present and warm
Process of elimination
OH- acts as a base and removes a hydrogen from the carbon neighbouring the carbon bonded to the halogen resulting in double bond forming between the carbons and heterolytic bond breaking of the carbon halogen bond releasing the halogen ions and water to form an alkene
When can there be a mixture of elimination products
If carbon chain is four or more carbon atoms in length and the halogen not attached to the terminal carbon a mixture of positional isomers may be formed
What temperature is elimination favoured
Hotter temperatures
When is substitution favoured
At lower temperatures
Is elimination more or less likely with tertiary and why
More likely due to steric hindrance
-react in elimination reaction with hydroxide ions more often than primary as the hydroxide group is blocked by the bulky R groups(steric hindrance) and the hydrogen that’s exposed is the one that is attacked rather than the carbon in the centre, in primary the hydroxide ion is much less hindered
Difference in conditions for elimination and to make an alcohol
For elimination to produce alkene use ethanol solvent and to produce alcohol aqueous ethanol solvent
Conditions that favour elimination
-ethanol solvent so no water
-higher temperatures
-concentrated solution of sodium hydroxide
Conditions that favour substitution
-lower temps
-more water in ethanol solvent
-less concentrated solution of sodium hydroxide
Substitution or elimination more likely in primary
Substitution
Substitution or elimination in secondary
Both elimination and substitution
