Question

Benzyne intermediate is not observed in:
(A)
(B)
(C)
(D)

Answer 1

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

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)

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)

Here, we can see that there is the presence of adjacent hydrogen alongside the leaving group, chlorine. So, benzyne can be formed.
(D)
 
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.