Question

Rank each group of compounds from most reactive to least reactive toward electrophilic aromatic substitution:b. 1-chloro-2,4-dinitrobenzene, 2,4-dinitrophenol, 1-methyl-2,4-dinitrobenzene

Accepted Answer

Step 1: Understand the concept of electrophilic aromatic substitution (EAS). EAS is a reaction where an electrophile replaces a hydrogen atom on an aromatic ring. The reactivity of the aromatic compound depends on the substituents already present on the ring, which can either activate or deactivate the ring toward electrophilic attack. Step 2: Analyze the substituents on each compound. Substituents can be electron-donating groups (EDGs) or electron-withdrawing groups (EWGs). EDGs increase the electron density on the aromatic ring, making it more reactive toward electrophiles, while EWGs decrease the electron density, making the ring less reactive. Step 3: For 1-chloro-2,4-dinitrobenzene, the substituents are a chlorine atom (weakly electron-withdrawing due to its inductive effect but slightly donating via resonance) and two nitro groups (strongly electron-withdrawing due to their -NO₂ groups). The nitro groups significantly deactivate the ring toward EAS. Step 4: For 2,4-dinitrophenol, the substituents are a hydroxyl group (-OH, a strong electron-donating group via resonance) and two nitro groups (strongly electron-withdrawing). The hydroxyl group partially counteracts the deactivating effect of the nitro groups, making this compound more reactive than 1-chloro-2,4-dinitrobenzene. Step 5: For 1-methyl-2,4-dinitrobenzene, the substituents are a methyl group (-CH₃, a weak electron-donating group via hyperconjugation) and two nitro groups (strongly electron-withdrawing). The methyl group slightly increases the reactivity of the ring compared to 1-chloro-2,4-dinitrobenzene but less so than the hydroxyl group in 2,4-dinitrophenol. Rank the compounds based on these observations.

Rank each group of compounds from most reactive to least reactive toward electrophilic aromatic substitution:
b. 1-chloro-2,4-dinitrobenzene, 2,4-dinitrophenol, 1-methyl-2,4-dinitrobenzene

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Concetti chiave

Electrophilic Aromatic Substitution (EAS)

Activating and Deactivating Groups

Ortho/Para vs. Meta Directing