19. Reactions of Aromatics: EAS and Beyond

Show how you would convert (in one or two steps) 1-phenylpropane to the three products shown below. In each case, explain what unwanted reactions might produce undesirable impurities in the product.

In the second propagation step in the bromination of toluene, Br₂ is only attacked by a radical on the substituent carbon. Why?

Predict the product of the following benzylic bromination reactions.

(c)

Show how you would convert (in one or two steps) 1-phenylpropane to the three products shown below. In each case, explain what unwanted reactions might produce undesirable impurities in the product.

For each compound, predict the major product of free-radical bromination. Remember that bromination is highly selective, and only the most stable radical will be formed.

(e)

Predict the product of the following benzylic bromination reactions.

(b)

Suggest reagents and reaction conditions that would result in synthesis of the following bromoalkanes.

(c)

Propose a mechanism for the bromination of ethylbenzene shown below.

The solvent tetrahydrofuran (THF) is often sold with a small amount of BHT added. Provide a mechanism that explains why this might be so.

Show the products you expect when each compound reacts with NBS with light shining on the reaction.

(d)

Predict the major products when the following compounds are irradiated by light and treated with (1) 1 equivalent of Br₂ and (2) excess Br₂.

(a) isopropylbenzene

(b)

(c) Based on what you know about the relative stabilities of alkyl radicals and benzylic radicals, predict the product of addition of HBr to 1-phenylpropene in the presence of a free-radical initiator.

(d) Propose a mechanism for this reaction.

A radical reaction, as it progressed through its propagation steps, involved the following radical species. Suggest which products might form in all possible termination steps (six products are possible).