15. REACTIONS OF AROMATIC COMPOUNDS. Electrophilic Aromatic Substitution.(approx. lecture time: 4 lectures)Topics covered: 15.1-15.14.
TNT, useful compound!Ibuprofen (Motrin, Advil), useful compound!
Electrophilic Aromatic Substitution
O2N NO2
NO2
CH3
O
OH
CH3
Examples of Electrophilic Aromatic Substitution
Mechanism of Electrophilic Aromatic Substitution
Reaction Coordinate Diagram
rate determining step
Bromination of Benzene
Thyroxine
Goiter, enlargement of the thyroid glad due to insufficient dietary iodine
(Human hormone that controls metabolism)
Made by electrophilic aromatic substitution of Iodine on tyrosine
Why do you need iodine in your diet?
Nitration of Benzene
HNO3 + H2SO4 O N O+
+ HSO3- + H2O
nitronium ion
Friedel-Crafts Alkylation of Benzene
Friedel-Crafts Alkylation of Benzene(Not necessary to start with alkyl halide; other possible functional groups can be used to generate a reactive carbocation)
Friedel-Crafts Alkylation of Benzene
Watch out for
rearrangements!
When the carbocation formed can rearrange to a more stable one, it does; the major products obtained from the reaction are those from the more stable carbocation.
Friedel-Crafts Acylation of Benzene
AlCl3
Cl
Cl
O O
O
AlCl3
O
Cl
O
AlCl3
O
H3C
CH3
some acyl groups
Mechanism
Friedel-Crafts Acylation of Benzene
Friedel-Crafts Alkylation and Acylation of Benzene (Additional Points to Remember)
Do not use them for Friedel-Crafts reaction
Aryl and vinyl halides cannot be used for Fridel-Crafts alkylations
Electrophilic Aromatic Substitution of Substituted Benzenes
(What happens when the benzene ring already has a substituent?)
Only one of two possible outcomes is observed:
1.
or
2.
The Effect of Activating and Deactivating Substituents
What happens when you carry out electrophilic substitution on a benzene with an activating substituent?
result is ortho and para substitution
What happens when you carry out electrophilic substitution on a benzene with an deactivating substituent? (** except for F, Cl, Br, I**)
result is meta substitution
What happens when you carry out electrophilic substitution on a benzene with a halogen (F, Cl, Br, I), which is weakly deactivating?
result is ortho and para substitution
Silent Spring (52nd anniversary)(How an aromatic organic compound started the environmental
movement)
“Silent Spring” is Rachel Carson’s book published in 1962 documenting the detrimental effects of pesticides (e.g., DDT) on birds and the environment. The book is considered to have started the environmental movement. DDT was later banned in 1972 in the US.
DDT, “DichloroDiphenyl-Trichloroethane”)
BPA, “bisphenol A”
Both of these compounds made by simple electrophilic aromatic substitution
HO OH
CH3H3C
Cl Cl
CCl3