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