Recognising how resonance contribtutes to the arrangement of charge around a ring helps to understand the reactivity of a substituted benzene.Consider the resonance contributors of ethoxybenzene According to resonance, is the ring: activated or deactivated to electrophilic substitution. And which site/s are the most susceptible to substitution?

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Begin by unpacking the effect of the ethoxy substituent on the benzene ring. The ethoxy group (-OEt) has lone pairs on oxygen that can participate in resonance with the aromatic ring, pushing electron density into the ring and making the ring more reactive toward electrophiles in general. This resonance donation makes the ring more activated relative to benzene itself, though the activating power is somewhat weaker than with a methoxy group due to the ethyl group reducing resonance donation slightly.

Option a: 'deactivated - meta positions are most active' is incorrect because the ethoxy substituent donates electron density via resonance, not withdraws it. Therefore it activates, not deactivates, the ring.

Option c: 'Activated - meta positions are most active' is incorrect because, for electron-donating substituents that donate by resonance (like -OEt), the most favorable positions for electrophilic attack are ortho and para, not meta. Meta substitution is favored by electron-withdrawing or resonance-deactivating groups, not by -OEt.

Option d: 'Deactivated - ortho and para positions are most active' is inconsistent: deactivation would reduce reactivity overall, and while ortho/para may be favored by the directing effects, a deactivated ring would not show such pronounced activity at those positions. This option contradicts the activating nature of the substituent.

Option b: 'Activated - ortho and para positions are most active' aligns with the known directing effect of electron-donating substituents like the ethoxy group: the ring is activated and the most reactive sites for electrophilic substitution are the ortho and para positions relative to the -OEt group. The resonance donation stabilizes the arenium ion more effectively at these positions, making them the primary sites for attack.

My LMS Subjects Practice LMS questions, Week 3

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