SECTION 15 ² ELECTROPHILIC AROMATIC SUBSTITUTION...
Transcript of SECTION 15 ² ELECTROPHILIC AROMATIC SUBSTITUTION...
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SECTION 15 ELECTROPHILIC AROMATIC SUBSTITUTION
15-1 -- The Chemistry of Benzene (C6H6)
15-1 -- General Mechanism of Electrophilic Aromatic Substitution (E.A.S.)
Delocalization of Charge
An Addition Reaction is Not Observed
15-2 -- Overview of Electrophilic Aromatic Substitution Reactions
Nitration (Adding NO2 to the Benzene Ring)
Sulfonation (Adding SO3H to the Benzene Ring)
Halogenation (Adding -X to the Benzene Ring)
Friedel-Crafts Alkylation (Adding -R to the Benzene Ring)
Friedel-Crafts Acylation (Adding -COR to the Benzene Ring)
15-3 -- The Nitration Reaction
Detailed Mechanism
Product is Nitrobenzene
15-3 -- The Sulfonation Reaction
Product is Benzenesulfonic Acid
Detailed Mechanism
Use of Fuming Sulfuric Acid
Le Chatelier s Principle and Possible Desulfonation
Principle of Microscopic Reversibility
15-5 -- Halogenation of Aromatic Rings
Product is a Halobenzene
Use of the Lewis Acid Catalyst, FeCl3
Detailed Mechanism
Iodination Mechanism is a Bit Different (CuCl2 as Catalyst)
15-6 -- Friedel-Crafts Alkylation
Doesn t Proceed on Aromatic Rings with Strongly Deactivating Substituents
Detailed Mechanism Works Well with R-Cl, R-Br, R-I, or R-F
Rearrangements of R and the Involvement of Free Carbocations
15-8 -- Friedel-Crafts Acylation
The Acyl Group
Detailed Mechanism
The Acylium Ion Not Prone to Rearrangement
15-9 -- Use H+ (D+) as the Electrophile
15-10 -- Directing Effects of Substituents
Ortho (o), Meta (m), and Para (p) Directors
Activators vs. Deactivators
Mechanism of Para Attack by an Electrophile
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Mechanism of Ortho Attack by an Electrophile
Mechanism of Meta Attack by an Electrophile
15-11 -- More on Activating, o,p-Directoring Groups
Electron-Withdrawing Induction vs. Resonance
15-13 -- More on Deactivating, m-Directoring Groups
15-13 -- Halogens are o,p-Directors and Weak Activators
15-14 -- Detailed Summary of Substituents Directing Effects
Activating, o,p-Directors (Both Strong and Weak)
Deactivatinig, m-Directors (Both Strong and Weak)
Deactivating, o,p-Directors (Weak)
15-14 -- Miscellaneous Notes About E.A.S Reactions
Important Side Notes on Friedel-Crafts Reactions
Ortho-Para Product Ratio is Sensitive to Steric Effects
Important Substituent Transformations (i.e. NO2 converted to NH2)
What if 2 or More Substituents Directing Effects Oppose Each Other?
15-17 -- Organic Synthesis of Benzene Derivatives
The Order of Reactions is Critical
15-18 -- Nucleophilic Aromatic Substitution Reactions (N.A.S.)
Mechanism #1: Addition-Elimination
Meisenheimer Complex
Need a Good Leaving Group (l.g.) and an Electron-Withdrawing Group
Mechanism #2: Elimination-Addition
Occurs via Benzyne Mechanism
Need a Very Strong Base
15-21 -- Benzyne Can Act as a Dienophile and React with Dienes
15-22 -- Side-Chain Oxidation Reactions (Use of KMnO4)
15-22 -- Benzylic Bromination Reactions
Occurs via a Free Radical Chain Mechanism
NBS = N-Bromosuccinimide
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SECTION 15 – ELECTROPHILIC AROMATIC SUBSTITUTION
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