• Electrophilic Addition: A reaction mechanism.
• Electrophile: It is a species that is attracted to an electron- rich centre, where it accepts a pair of
electrons to form a covalent bond. Usually a positive ion or contains δ+ charge. It can be something
like HBr- don’t get confused with radical substitution with alkanes.
• Double Bond: The double bond in alkene is region of high electron density due to π- electrons
which attracts electrophiles.
• Remember where arrows go, remember minus charge. Remember dipoles.
1- Top atom is more electronegative than bottom atom- a polar molecule. Acts as an
electrophile.
2- Electron pair in π- bond is attracted to partially positive top atom, causing double bond to
break.
3- Bond forms between top atom and a carbon atom in double bond.
4- The Br- Br molecule breaks by hetrolytic fission, with electron pair going to bottom δ- atom.
5- The bottom atom forms ion- Br-
. Carbocation formed- positively charged carbon atom.
6- The bottom atom reacts with carbocation to form final product.
• Curly Arrows: Have to start arrow precisely at the bond or lone pair of electrons and precisely to
atom which the electron pairs transfers. No gaps.
• Induced Dipole: When non- polar molecules like Br- Br approach the alkene, an induced dipole is
formed. From bonded pair of electrons being equally distributed between two atoms, the
electrons are repelled. Top end becomes Brδ+ and bottom end becomes Brδ-
.
• Two Products Formed: Reaction with unsymmetrical molecule with H- X so two products formedisomers.
• Carbocations: Primary carbocation- positive charge is on carbon atom at end of chain. Secondary
carbocation- positive charge is on carbon electron with two carbon chains attached. Tertiarythree R/ alkyl groups attached (no hydrogens attached) to positively charged carbon atom.
• Markownikoff’s Rule: Know spelling. Tertiary as most stable. Then secondary most stable. Primary
least. Major product is most stable.