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Benzyne intermediate is not observed in:
(A) 168飞艇 c647022631a8385f57308d5120760fc7
(B) 168飞艇 ed0d6d5254b568f6b377505711a09618
(C) 168飞艇 2af6f310ef7c01a29cacbbf5284078dc
(D) 168飞艇 be6695a17e97de13a4ee8e7169564e80


Answer
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303.3k+ views
Hint: The structure requires a leaving group and a hydrogen atom at the adjacent carbon to the carbon which is bearing the leaving group. A good leaving is usually a weak base. Benzyne involves a C-C triple bond in its structure.

Complete step by step solution:
-Benzyne is a six-member hydrocarbon ring involving two double bonds and a C-C triple bond.
-In the mechanism of formation of benzyne, it is necessary for the structure to have a good leaving group. Alongside a good leaving group, it is also necessary to have a hydrogen atom at adjacent carbon which can leave to form benzyne. In short, we can show the formation of benzyne as
168飞艇 996847a91ef9b755f8832fb1a3db80a2
Here LG is leaving the group.
Let’s see the compounds given in all the options in order to find which one will not give benzyne.
(A)
168飞艇 423d08c0541d87045fc0b3450c17a9f6
So, in this case, benzyne intermediate can be formed as $ - OC{H_3}$ is a good leaving group and there is a hydrogen atom at the adjacent carbon of the leaving group.
(B)
 In this structure, there is a chlorine group which can act as a leaving group but there is no hydrogen atom with the adjacent carbon bearing the leaving group. So, this compound cannot give benzyne intermediate.
(C)
168飞艇 ecbe3e44ea4c147f4d1d1da2ff14b739
Here, we can see that there is the presence of adjacent hydrogen alongside the leaving group, chlorine. So, benzyne can be formed.
(D)
 168飞艇 df0c2182b975aa0c9d09bc87b902373e
Here, ${N_2}^ + $ group can act as a good leaving group and there is a hydrogen atom at adjacent carbon bearing the leaving group. So, benzyne formation is also possible here.

Therefore, the correct answer is (B).

Note: Remember that in option (A), there are a total of two groups –F and methoxy group. Here, -F is a strong base and methoxy group is a weaker base. So, as weaker bases are good leaving groups, it will leave and form benzyne in suitable conditions.