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Chapter 23: Aryl Halides



Summary | Aryl Halides | Preparations of Aryl Halides | Reactions of Aryl Halides | Benzyne | Self Assessment | Quiz |


Benzyne

Chapter 23: Aryl Halides

Structure
 

Benzyne
Benzyne is an example of an aryne (-yne = triple bond)
This is no ordinary triple bond as the second p interaction results from a weak interaction of sp2 hybrid orbitals lying in the plane of the ring.
The triple bond is non-linear due to the constraints of the 6-membered ring.
Benzyne is strained and highly reactive.
orbitals involved in the triple bond in benzyne

Reactivity

electrostatic potential of benzyne The image shows the electrostatic potential for benzyne. 
The more red an area is, the higher the electron density and the more blue an area is, the lower the electron density. 

Here we see the triple bond as a region of high electron density (red). 
As a result of the non-linear triple bond, benzyne is highly reactive.
Benzyne is a reactive intermediate, an tends to undergo addition reactions.

Addition Reactions of Benzyne

addition of NH3 to benzyne
addition of H2O to benzyne
Reaction type : elimination then addition

Summary

Related Reactions
MECHANISM OF THE ADDITION OF AMMONIA TO BENZYNE
Step 1:
The N in amide functions as the nucleophile and attacks the reactive triple bond C in benzyne creating the new C-N bond and an intermediate carbanion.
mechanism for the addition of ammonia to benzyne
Step 2:
An acid/base reaction. Rapid protonation of the reactive carbanion from the ammonia forms the aniline and another molecule of the amide ion.
 

Diels-Alder Reactions of Benzyne

Diels-Alder reaction of benzyne

 
Dienophile
Diene
Product
alternate benzyne generation


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