Substituent Effects - Induction Inductive effect – movement of electron density through sigma bonds, based on electronegativity Example – inductive effect on a carbocation Cation Cation Stabilized Cation Destabilized alkyl group donates electron density, stabilizes carbocation -CF3 group removes electron density, destabilizes carbocation

Inductive Effects Controlled by electronegativity and polarity of bonds in functional groups Alkyl groups donate electrons by induction

Inductive Effects Controlled by electronegativity and polarity of bonds in functional groups Halogen (-X), -C=O, -CN, -CF3, -SO3H and -NO2 groups withdraw electrons inductively through sigma bonds. (-OR and -NH2 groups also withdraw by induction)

Substituent Effects - Resonance Resonance effect – movement of electrons through pi bonds, based on conjugation Example – resonance effect donating electron density Cation Cation Stabilized by Resonance oxygen can donate electron density via resonance using its lone pairs

Resonance Effects – Electron Donation Halogen, -OH, alkoxyl (-OR), and amino (-NH2) substituents donate electrons electrons flow from substituents into the ring Effect is greatest at ortho and para positions any lone pair on atom next to ring can donate e- density by resonance

Substituent Effects - Resonance Resonance effect – movement of electrons through pi bonds, based on conjugation Example – resonance withdrawing electron density Benzene Carbonyl Substituent Which ring has more e- density? Carbonyl group – gives the ring a partial plus charge

Resonance Effects – Electron Withdrawal -C=O, -CN, -SO3H, and -NO2 substituents withdraw electrons from the aromatic ring by resonance  electrons flow from the ring to the substituent These aromatic rings all have less electron density than benzene itself due to the electron-withdrawing substituent.

Substituent Effects Q. How do different substituents influence the rate of electrophilic aromatic substitution reactions? (activate or deactivate the ring) Q. How do different substituents effect the orientation of the substitution reaction? (ortho/para vs. meta substitution) Answer: Inductive Effects Resonance Effects x