Briefly explain why the given structure is unstable.

What is the benzyne intermediate if H_a is the proton removed in the first step of the benzyne mechanism? What are the two products of the reaction?

If the nucleophilic aromatic substitution reaction below occurs via a benzyne mechanism, predict the products.

Propose a mechanism to show how a mixture of meta and para-substituted products are obtained from the reaction of p-chlorocumene (1-chloro-4-isopropylbenzene) with sodium hydroxide at 350 °C.

The last step in the reaction below is a Diels-Alder reaction. Propose a plausible mechanism for the formation of the dienophile in the reaction.