Electrophillic Addition Flashcards
What is an electrophile?
Electron pair acceptor
What happens during an electrophilic addition reaction?
- double bond in an alkene represents a region of high electron density due to pi electrons
- electrophiles are attracted to these pi electrons
Describe the electrophilic addition of hydrogen bromide to an alkene.
- Electron pair in the pi bond is attracted to the slightly positive hydrogen atom so the double bond breaks and a new bond forms between one of the carbon atoms and the hydrogen atom
- H-Br bond breaks by heterolytic fission with the electron pair going to bromine
- A bromide ion and a carbocation are formed
- Positively charged carbocation is unstable so quickly reacts with the bromide ion forming a halogenoalkane
What do curly arrows represent?
The movement of a pair of electrons
Describe the electrophilic addition of bromine to an alkene.
- Electron pair in the pi bond is attracted to the slightly positive bromine atom, causing the double bond to break.
- A new bond forms between one of the carbon atoms and the bromine atom
- The Br-Br bond breaks by heterolytic fission and the electron pair goes to the other bromine atom
- This forms a negative bromide ions and a positive carbocation
- The carbocation is unstable and quickly reacts with the bromide ions to form a halogenoalkane
Where is the positive charge in a primary and secondary carbocation?
Primary = the carbon atom the end of the chain with only one other carbon atoms attached
Secondary = a carbon atom with two carbon atoms attached
What is the order of stability of the carbocations?
Tertiary > secondary > primary
What property makes a carbocation more stable?
The more alkyl groups, the more the charge is spread out, making the ion more stable
Through which carbocation is the major product produced?
The more stable carbocation
Eg. secondary or tertiary
