Aromatic Nucleophilic Substitution Reactions.pdf

The contents of this presentation is as follow-
1. Introduction aromatic nucleophilic substitution SNAr, SN1 , Benzyne and SRN1 mechanisms
2. Reactivity effect of substrate structure leaving group and attacking nucleophile
3. The Von Richter,
4. Sommlet-Hauser
5. Smiles rearrangements.

1. Lecture Delivered By
Mr. Nilkesh K. Dhurve
Assistant Professor
Department of Chemistry
Shri Pundlik Maharaj Mahavidyalaya Nandura Rly, Dist-Buldana 22-Jan-22 1

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•Introduction aromatic nucleophilic substitution SNAr, SN1 , Benzyne and SRN1 mechanisms,
•Reactivity effect of substrate structure leaving group and attacking nucleophile,
•The Von Richter,
•Sommlet-Hauser
•Smiles rearrangements.

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When aromatic compounds react with nucleophilic they generally do so by nucleophilic aromatic
substitution reaction(S
NAr).
Reason:
SN
2
at sp
2
C does not occur.
What about SN
1
?

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Addition-Elimination Mechanism:
The electrons must be able to get out of the ring into anion stabilizing group.
Conjugated Substitution
Reaction
Nucleophilic Substitution
Reaction

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General Reaction: A typical nucleophilic aromatic substitution has:
An O-, N- or CN- nucleophile
A halide for leaving group
A carbonyl, nitro, or cyanide group ortho or para to
the leaving group(Activating Group) Mechanism:
Cl

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Example-1:
Example-2:

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The intermediate in the addition-elimination mechanism:
Anion delocalized over five sp
2
-hybridized carbon of six membered ring.
Sixth carbon, the point at which the nucleophile attacked, is sp
3
hybridized.

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The intermediate in the addition-elimination mechanism:
A larger shift means less electronic shielding and a smaller shift means more electronic shielding.

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Example:
Mechanism:

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The leaving group and the mechanism:

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The leaving group and the mechanism:

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The activating anion stabilizing substituent:
Example:

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The activating anion stabilizing substituent:
Example: The trifluoromethyl group works by using only its powerful inductive effect.

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Examples:
Iodine is not reactive enough to attack the benzene
rings, but adding potassium iodide to the diazonium
salt give an aryl iodide by nucleophilic aromatic
substitution.

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Elimination-Addition Mechanism:
Low Temp.,
Strong Base
High Temp.,
Mechanism:

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Elimination-Addition Mechanism:
Any nucleophile basic enough to remove the ortho proton can carry out the reaction.

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Examples:
Mechanism:
Reason for the meta-product- 1) Electronic factor; 2) Steric factor

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Examples:
Mechanism:

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Evidence for this mechanism comes from trapping experiments:
Diels-Alder Cycloadduct

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General Reaction:
Mechanism:

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Example-1:
Example-2:

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General Reaction:
Mechanism:

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Example-1:
Example-2:

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General Reaction:
Mechanism:

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Example-1:
Example-2:

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