1. Drill and practice with on-ring aromatic substitutions
Class of substitution reaction most commonly occurring on a benzene
Electrophilic aromatic substitution
What key reactant species must be generated in all five of the classic aromatic substitutions on benzene?
A very powerful (positively charged) Lewis acid
A Lewis acid is….
An electron acceptor
Another `affectionate’ name for the Lewis acid in aromatic substitutions is:
electrophile
Fyi…phile is Greek for lover

2. Br+ CH3+ Lewis acid responsible for aromatic bromination:
Drill and practice with on-ring aromatic substitutions (cont.)
Lewis acid responsible for aromatic bromination:
Br+
Reagents & solvent used to make Br+
Fe or FeBr3 with Br2 in acetic acid
Reaction leading to Br+ ?
FeBr3 +Br2 FeBr4- +Br+
Lewis acid attacking benzene (Ar) to make methyl benzene: ArCH3 [Ar=aryl=> benzene group ]
CH3+
Reagents & solvent (if any) used to make CH3+
AlCl3 with CH3Cl neat
Reaction leading to CH3+ ?
AlCl3 +CH3Cl AlCl4- +CH3+
Special name for ring alkylation reaction
Friedel-Crafts alkylation

3. Lewis acid responsible for aromatic sulfonation:
Drill and practice with on-ring aromatic substitutions (cont.)
HSO3+
Lewis acid responsible for aromatic sulfonation:
Reagents & solvent used to make HSO3+
SO3 in H2SO4 (fuming sulfuric acid)
Reaction leading to HSO3+ ?
H2SO4 +SO3 HSO4- + HSO3+
AlCl3 +
neat
What is the electrophile generated in the reaction above ?
Reaction leading to ?

4. Special name for ring acylation reaction Friedel-Crafts acylation
Drill and practice with on-ring aromatic substitutions (cont.)
Special name for ring acylation reaction
Friedel-Crafts acylation
Conc. HNO3 + trace conc. H2SO4
NO2+
What is the electrophile generated in the reaction above ?
Reaction leading to NO2+ ?
HNO3+HNO3 NO3- + NO2+ + H2O
NaOH
300 oC
H+/H2O

5. All other deactivating groups direct…
Drill and practice with on-ring aromatic substitutions (cont.)
SnCl2 or Fe
with H+
NaOH
Activating groups direct…
o and p
(ortho and para)
Halogens are de-activating and direct…
o and p
(ortho and para)
All other deactivating groups direct…
m (meta)
Activating groups are electron….
Donors
Dectivating groups are electron….
Acceptors

6. An Activating group on a ring
Drill and practice with on-ring aromatic substitutions (cont.)
An Activating group on a ring
decreases increases the rate of substitution on the ring
Too much Steric hindrance
CH3 is activating (o,p directing)
NO2 is de-activating (m directing)
NH2 is activating
Most likely species formed

7. C6H6 lately? He hasn’t benzene for a while….

8. Cats love all ringie thingies !

9. From rubric for Friedel-Crafts Theory (30 points total)
Step 2: Initial electrophilic aromatic attack to
form t-butylbenzene
___ /6 Clear explanation with pix for how Lewis acid disrupts
the aromatic ring. Electron pushing protocol is strongly
suggested.It is suggested that you use static Kekule
resonance structures which provide specific images
of how (+) charge migrates around disrupted ring.
___/ Clear explanation with pix of how H is expelled and
initial t-butyl benzene is formed. Again, electron pushing
model is preferred

10. Step 4: o,p Directed attack to form 1,2 or 1,4-ditertbutyl benzene (o,p directing)
___ /5 explanation with pix of how activating t-butyl group on
benzene produces o and p direction in interrupted ring
(this is why the static Kekule structures are preferred above).
Electron pushing should remain the mode of explanation
___ /3 explanation of why 1,4-ditertbutylbenzene is favored