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Solutions to Problems Aryl Halides

Building Bridges to Knowledge

Photo of a bridge in proximity to Walla Walla, Washington

1. Predict the major products for the following reactions.

(a)

2

(b)

(c)

3

2. When sodium methoxide is added to 2,4-dinitrobromobenzene, the proton magnetic resonance spectrum changes as indicated below. What explanation can you provide for the change in the proton magnetic spectrum.

Proton NMR for 2,4-dinitrobromobenzene

Proton NMR after 2,4-dinitrobromobenzene is treated with sodium methoxide.

The methoxide nucleophilic attacks the aromatic nucleus generating a Meisenheimer complex where the aromaticity has been disrupted.

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3. Suggest the possible products expected when 2-iodoaniline is

treated with sodium amide in ammonia.

4. Pyrrolidine reacts with α-iodonapthalene to form a single product,

and pyrrolidine reacts with β-iodonapthalene to form an isomer of the compound that is formed when α-iodonapthalene reacts with pyrrolidine. However, sodium pyrrolidide reacts with α-iodonapthalene or β-iodonapthalene to form two isomers rather than a singe isomer. Give a reasonable explanation for these observations.

pyrrolidine α-iodonapthalene β-iodonapthalene

The pyrrolidine forms a Meisenheimer complex with both α and β iodonapthalenes, and then the Meisenheimer complexes re-aromatizes to form the substituted pyrrolidinyl napthalenes.

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α-pyrrolidinylnapthalene and

β-pyrrolidinylnapthalene A hydrogen atom is abstracted by sodium pyrrolidide, a strong base, to form a benzyne derivatives; consequently, two isomers are formed from nucleophilic attack on the benzyne derivatives.

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5. Suggest a mechanism for the following reaction.

(1)

(2)

8

(3)

6. Write a mechanism for the following reaction.

(1)

(2)

9

(3)