Electrophilic attack at C=C
Electrophile: an electron-pair acceptor.
The electron-rich C=C bond attracts electrophiles, allowing alkenes to undergo electrophilic addition.
During an addition reaction, the C=C becomes a C–C single bond while new bonds form to the two carbon atoms.
Electrophile approaches
The high electron density of the double bond attracts the electrophilic centre.
Carbocation forms
An electron pair from C=C forms a new bond, leaving a positively charged carbon intermediate.
Second species adds
A negatively charged species donates an electron pair to the carbocation, completing the addition.
A carbocation is an intermediate containing a positively charged carbon atom.
Exam Tip: In an electrophilic-addition mechanism, show electron-pair movement from the C=C bond towards the electrophile and include the carbocation intermediate.