19. Reactions of Aromatics: EAS and Beyond

What are the products of the following reactions?

b.

We have considered nucleophilic aromatic substitution of pyridine at the 2-position and 3-position but not at the 4-position. Complete the three possible cases by showing the mechanism for the reaction of methoxide ion with 4-chloropyridine. Show how the intermediate is stabilized by delocalization of the charge onto the nitrogen atom.

(b) When 3-bromopyridine is used in this reaction, stronger reaction conditions are required and a mixture of 3-aminopyridine and 4-aminopyridine results. Propose a mechanism to explain this curious result.

Suggest an arrow-pushing mechanism of the following rearrangement.

Predict the product of the following substitution/addition reactions involving phenoxides. [Because this problem represents a review of current and previous material, section numbers have been provided for your reference.]

(d)

Propose mechanisms and show the expected products of the following reactions.

(c) p-nitrobromobenzene + methylamine (CH₃–NH₂)

(d) 2,4-dinitrochlorobenzene + excess hydrazine (H₂N–NH₂)

What are the products of the following reactions?

e.

Rank the following compounds from greatest tendency to least tendency to undergo nucleophilic aromatic substitution:

chlorobenzene 

1-chloro-2,4-dinitrobenzene 

p-chloronitrobenzene

Show how you would accomplish the following syntheses.

(c) benzene → p-methoxybenzaldehyde

How do the mechanisms of the following reactions differ?

Propose a mechanism for each of the following reactions:

b.