0
$\begingroup$

During Fries Rearrangement, oxygen donates its lone pair to $\ce{AlCl_3}$ forming $\ce{-O^+-AlCl3}$. Since this is a strong electron withdrawing group, shouldn't the final product be meta-substituted?

$\endgroup$
1
  • $\begingroup$ Phenoxide ions are typically electron donating though? $\endgroup$ – Schwarz Kugelblitz Jul 6 '20 at 11:16
3
$\begingroup$

enter image description here

The above is the mechanism for Fries Rearrangement for a brominated ester( doesn't matter really, for any ester the mechanism essentially remains to be the same).As per what I infer from your question, I think you mean to ask why even in the presence of $\ce{O^+-AlCl3}$ which is a strongly deactivating group, the major product is not meta-substituted.

As you can clearly see, in the next step itself a stable acylium is formed and the formal charge on $\ce{O}$ is no longer positive.So, as phenoxide ion is an activating group and o,p-director, two possible products are expected which are ortho and para substituted.However, at higher temperatures, the major product is ortho substituted which is driven by chelation.

NOTE:

As far as I know, both intramolecular and intermolecular reaction mechanisms are able to explain the major products and it is still not confirmed which one is the actual mechanism.

Image source:

https://www.synarchive.com/named-reactions/fries-rearrangement

$\endgroup$
4
  • $\begingroup$ @Niescte Does this answer your query? $\endgroup$ – Chem-Learner Jul 6 '20 at 12:22
  • $\begingroup$ Such ping doesn't work chemistry.meta.stackexchange.com/questions/3889/… $\endgroup$ – Mithoron Jul 6 '20 at 15:57
  • $\begingroup$ @Mithoron Niescte has asked this question and I was not sure if I understood Niescte's question correctly.So, wanted to confirm with the author of the post, whether I interpreted in the correct way.If this is against the policy of the community, then I can delete that comment $\endgroup$ – Chem-Learner Jul 6 '20 at 16:31
  • $\begingroup$ sigh You'd have to comment under his question or comment, otherwise it just doesn't ping, that's my point - check out the meta stuff I linked for more info about pinging. BTW asking about clarification, before answering would be better... $\endgroup$ – Mithoron Jul 6 '20 at 22:48

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.