6.27 - The mechanisms of addition reactions Flashcards
What is crucial about the arrows used in mechanisms?
They must be curly
What do curly arrows represent?
The transfer of electrons
What does a double-headed curly arrow represent?
The transfer of 2 electrons
What is an electrophile?
A species attracted to an area of high electron density
What type of reaction is the reaction of hydrogen bromide and ethene?
Electrophilic addition
Why?
Because the hydrogen bromide molecule acts as an electrophile, and it is an addition reaction
What is step 1 of the mechanism?
- Curly arrow from C=C bond to H atom
- Curly arrow from middle of H-Br bond to Br atom
- Hydrogen added to the left carbon
- Right carbon becomes a carbocation
- Bromine ion formed
What is step 2 of the mechanism?
- Arrow from bromine ion to carbocation
- Bromine bonds to carbon
What is heterolytic fission?
The breaking of a covalent bond so that both bonding electrons are taken by one atom
What happens when the molecule is unsymmetrical?
A major or minor product will be formed
What are the 3 types of carbocation?
Primary, secondary and tertiary
Which type of carbocation is most stable?
Tertiary, as the charge is spread out more evenly
What is the major product formed from?
The more stable carbocation
What is the minor product formed from?
The less stable carbocation
What is an example of an unsymmetrical molecule?
Propene, as it has 3 carbon atoms, and a double bond
