19. Reactions of Aromatics: EAS and Beyond

Predict the major products formed when benzene reacts (just once) with the following reagents.

f. fuming sulfuric acid

Biphenyl is two benzene rings joined by a single bond. The site of substitution for a biphenyl is determined by (1) which phenyl ring is more activated (or less deactivated), and (2) which position on that ring is most reactive, using the fact that a phenyl substituent is activating and ortho, para-directing.

a. Use resonance forms of a sigma complex to show why a phenyl substituent should be ortho, para-directing.

(i)

Biphenyl is two benzene rings joined by a single bond. The site of substitution for a biphenyl is determined by (1) which phenyl ring is more activated (or less deactivated), and (2) which position on that ring is most reactive, using the fact that a phenyl substituent is activating and ortho, para-directing.

b. Predict the mononitration products of the following compounds

(iv)

Biphenyl is two benzene rings joined by a single bond. The site of substitution for a biphenyl is determined by (1) which phenyl ring is more activated (or less deactivated), and (2) which position on that ring is most reactive, using the fact that a phenyl substituent is activating and ortho, para-directing.

b. Predict the mononitration products of the following compounds

(v)

Biphenyl is two benzene rings joined by a single bond. The site of substitution for a biphenyl is determined by (1) which phenyl ring is more activated (or less deactivated), and (2) which position on that ring is most reactive, using the fact that a phenyl substituent is activating and ortho, para-directing.

b. Predict the mononitration products of the following compounds

(vi)

Step 2 of the iodination of benzene shows water acting as a base and removing a proton from the sigma complex. We did not consider the possibility of water acting as a nucleophile and attacking the carbocation, as in an electrophilic addition to an alkene. Draw the reaction that would occur if water reacted as a nucleophile and added to the carbocation. Explain why this type of addition is rarely observed.

Propose a mechanism for the sulfonation of pyridine, and point out why sulfonation occurs at the 3-position.

Show how m-toluidine can be converted to the following compounds, using any necessary reagents.

(e)

The first step of a reaction called electrophilic aromatic substitution is as follows:

If this step is rate-determining for the overall reaction, which benzene derivative would you expect to react most quickly? Which would react most slowly?

(a)

The nitro group directs electrophilic aromatic substitution to the meta position. After reduction by hydrogenation, to which carbon(s) does it direct?

Predict the major product of the following electrophilic aromatic substitution reactions.

(b) 

Predict the major products formed when benzene reacts (just once) with the following reagents.

(i) iodine + HNO₃

Predict the major products formed when benzene reacts (just once) with the following reagents.

d. bromine + a nail

Draw the product(s) of each of the following reactions:

a. benzoic acid + HNO₃/H₂SO₄

b. isopropylbenzene + Cl₂ + FeCl₃

What is the major product(s) of each of the following reactions?

e. nitration of p-methoxybenzaldehyde

f. nitration of p-tert-butylmethylbenzene