Hepworth, Waring and Waring (2002) mentions that:

In general, electron-withdrawing substituents make the arene more susceptible to reduction, while the opposite applies for electron-donating substituents.

They then go on to say:

Methoxybenzene (anisole) is reduced more rapidly than benzene under Birch conditions. This is an exception to the rule, the reasons for which are not clear.

Why is this the case? Does anyone know of any possible explanations?

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Source: Wikipedia Commons

Also, I was thinking, since the methoxy group donates electron density mesomerically to the ortho and para positions, wouldn't it be unfavourable for the carbanion to form that the ortho positions? This seems to happen in the mechanism shown above.

Lastly, I understand that the dispute between whether it is "Mechanism O" or "Mechanism M" was settled a while ago but I've read that the evidence pointing to "Mechanism O" seems to be computational studies and experiments. However, there has yet to be any qualitative explanations, based on chemistry principles and concepts, as to why "Mechanism O" is the one which occurs to a greater extent. I was wondering if anyone knows of any such explanations?


Hepworth, J. D., Waring, D. R., & Waring, M. J. (2002). Aromatic Chemistry. United Kingdom: The Royal Society of Chemistry.

  • 2
    $\begingroup$ You have very good questions but in my opinion it would be better to split them up. Two of your three questions are research level (which may not actually have an answer!) and fully deserve to stand on their own. $\endgroup$ – orthocresol Feb 18 '18 at 19:37
  • $\begingroup$ @orthocresol I understand the first and third questions are somewhat research-level. I don't really expect complete answers for these questions but I do hope to get some insightful input from some users. As for my second question, I definitely do expect an answer as it is more of a beginner-learning-a-new-topic kind of question. $\endgroup$ – Tan Yong Boon Feb 19 '18 at 1:08
  • $\begingroup$ People can feel free to just answer one of the three questions when responding and I will accept the most comprehensive and insightful of them. $\endgroup$ – Tan Yong Boon Feb 19 '18 at 1:10

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