Question

Predict the site(s) of electrophilic attack on these compounds.

Accepted Answer

Step 1: Analyze the substituents on the aromatic ring for compound (a). The hydroxyl group (-OH) is an electron-donating group through resonance and inductive effects, activating the ring towards electrophilic attack. The nitro group (-NO₂) is an electron-withdrawing group through resonance and inductive effects, deactivating the ring and directing electrophilic attack to meta positions relative to itself. Step 2: Determine the directing effects for compound (a). The -OH group is an ortho/para-directing group, while the -NO₂ group is a meta-directing group. The competition between these groups will influence the site of electrophilic attack. Step 3: For compound (a), predict the most likely sites of electrophilic attack. The -OH group will activate the ortho and para positions relative to itself, but the para position is less sterically hindered. The -NO₂ group will deactivate the ortho and para positions relative to itself, favoring meta positions. Step 4: Analyze the substituents on the aromatic ring for compound (b). The methoxy group (-OCH₃) is an electron-donating group through resonance and inductive effects, activating the ring towards electrophilic attack. The methyl group (-CH₃) is also an electron-donating group, but its effect is weaker compared to -OCH₃. Step 5: Determine the directing effects for compound (b). Both -OCH₃ and -CH₃ are ortho/para-directing groups. The -OCH₃ group will strongly activate the ortho and para positions relative to itself, while the -CH₃ group will activate its own ortho and para positions. The most likely sites of electrophilic attack will be the positions that are activated by both groups or are sterically favorable.

Predict the site(s) of electrophilic attack on these compounds.

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Concetti chiave

Electrophilic Aromatic Substitution (EAS)

Activating and Deactivating Groups

Ortho/Para vs. Meta Directing Effects