Question

List the compounds in each set from most reactive to least reactive toward electrophilic aromatic substitution:a. benzene, phenol, toluene, nitrobenzene, bromobenzene

Accepted Answer

Step 1: Understand the concept of electrophilic aromatic substitution (EAS). EAS involves the attack of an electrophile on an aromatic ring, and the reactivity depends on the substituents attached to the ring. Electron-donating groups (EDGs) increase reactivity by activating the ring, while electron-withdrawing groups (EWGs) decrease reactivity by deactivating the ring. Step 2: Analyze the substituents on each compound. Benzene (I) has no substituents, phenol (II) has an -OH group (strong EDG), toluene (III) has a -CH3 group (weak EDG), nitrobenzene (IV) has a -NO2 group (strong EWG), and bromobenzene (V) has a -Br group (weak EWG). Step 3: Rank the substituents based on their activating or deactivating effects. The -OH group in phenol is the strongest activator, followed by the -CH3 group in toluene. Benzene is neutral, while -Br in bromobenzene is a weak deactivator, and -NO2 in nitrobenzene is the strongest deactivator. Step 4: Arrange the compounds from most reactive to least reactive toward EAS based on the substituents' effects. Phenol (II) will be the most reactive due to the strong activation by the -OH group, followed by toluene (III), benzene (I), bromobenzene (V), and finally nitrobenzene (IV) as the least reactive due to the strong deactivation by the -NO2 group. Step 5: Verify the reasoning by considering resonance and inductive effects. The -OH group in phenol donates electrons through resonance, greatly activating the ring. The -CH3 group in toluene donates electrons via hyperconjugation, moderately activating the ring. Benzene has no substituents, so it is neutral. The -Br group in bromobenzene withdraws electrons weakly via inductive effects, slightly deactivating the ring. The -NO2 group in nitrobenzene strongly withdraws electrons via resonance and inductive effects, making it the least reactive.

List the compounds in each set from most reactive to least reactive toward electrophilic aromatic substitution:
a. benzene, phenol, toluene, nitrobenzene, bromobenzene

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Concetti chiave

Electrophilic Aromatic Substitution (EAS)

Activating and Deactivating Groups

Resonance and Stability