3.3.10.2 Electrophilic Substitution
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What reactions does benzene undergo?
It only undergoes substitution, not addition
What can the NO2 be replaced by in nitrobenzene?
Any electrophile
What are friedel - crafts acylation reactions?
When AlCl3 is added
What do activating groups do?
Activate the ring
What do deactivating groups do?
Deactivate the ring
At what rate is the second and third NO2 group added?
2nd: added slower because electron density is pulled towards the withdrawing group 3rd: slower ^ ^ ^ ^ ^ ^ ^
What is the nucleophile for nitration?
+ NO2
What is the nucleophile for acylation?
+ C = O | R
What is the nucleophile for halogenation?
X2
What is the nucleophile for addition?
H2
What is the nucleophile for alkalation?
+CH3
Why does benzene burn with a sooty flame?
It has a high carbon to hydrogen ratio This leaves unburnt carbon which produces soot
Why does benzene undergo electrophilic substitution and not addition?
Addition would require enough energy to destroy the aromatic system
What is the mechanism for the electrophilic substitution of arenes?
See card
What are the Friedel-Crafts acylation reactions?
Aluminium chloride acts as a catalyst RCO substitutes with a hydrogen Acyl chlorides provide the RCO group
What is an electrophile?
A positive ion or the positive end of a dipole
What are the electrons in a benzene ring attracted to?
Electrophiles (positive)
What is the nitration reaction of arenes?
The substitution of an NO2 group for one of the hydrogen atoms The NO2+ electrophile is generated by concentrated nitric and sulfuric acids Sulfuric acid donates a proton to HNO3 to form H2NO3 H2NO3 then loses a molecule of water to give NO2 (nitronium or nitryl cation)
What are examples of electron withdrawing groups?
NO2, COCl
What are examples of electron releasing groups?
CH3, OCH3, OH, NH2
What are electron withdrawing groups and what do they do?
They withdraw electrons from the ring, making it less susceptible to further electronic substitution They direct further substitution to the 3rd and 5th positions
What are electron releasing groups and what do they do?
They release electrons onto the benzene ring and therefore make it more susceptible to further electrophilic substitution reactions They direct further substitution to the 2nd, 4th and 6th positions on the ring
What are the Friedel crafts acylation reactions?
Aluminium chloride catalyst Substitution reaction with an RCO group substituting for a hydrogen on the aromatic ring
How is the nitrate ion formed from sulfuric and nitric acids?
HNO3 + 2H2SO4 = NO2+ + H3O+ + 2HSO4-