August 11, 2020, 06:44:44 AM
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Topic: If Fluorine is an electron withdrawing group, why is it an Ortho_Para director?  (Read 216 times)

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Offline JoeyBob

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All other non-halogen withdrawing groups seem to be meta directors?

Unlike of other withdrawing groups, would Fluorine destabilize aldehydes because of this different character?

Online chenbeier

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Not only fluorine also all other halogen have this behaviour.

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Electron donating groups are generally ortho/para directors for electrophilic aromatic substitutions, while electron withdrawing groups are generally meta directors with the exception of the halogens which are also ortho/para directors as they have lone pairs of electrons that are shared with the aromatic ring. .

https://en.m.wikipedia.org/wiki/Electrophilic_aromatic_directing_groups?sa=X&ved=2ahUKEwjStLblsJ3oAhUH2aQKHbvMAbMQ9QF6BAgDEAI

Offline hollytara

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sigma withdrawing but pi donating. 

Both are relatively weak effects.  The withdrawing deactivates overall, but the donation makes ortho and para reaction faster.

Note that fluorine is most electronegative, but the pi orbitals match better with carbon.  As electronegativity decreases (F-Cl-Br-I) and withdrawing effect decreases, size increases and donating effect also decreases so all halogens are about the same. 

Offline JoeyBob

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Not only fluorine also all other halogen have this behaviour.

Quote
Electron donating groups are generally ortho/para directors for electrophilic aromatic substitutions, while electron withdrawing groups are generally meta directors with the exception of the halogens which are also ortho/para directors as they have lone pairs of electrons that are shared with the aromatic ring. .

https://en.m.wikipedia.org/wiki/Electrophilic_aromatic_directing_groups?sa=X&ved=2ahUKEwjStLblsJ3oAhUH2aQKHbvMAbMQ9QF6BAgDEAI

I did say "All other non-halogen.." Should be obvious that I'm not only talking about fluorine having this behavior when I say that.

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