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Chemistry Forums for Students => Organic Chemistry Forum => Topic started by: JoeyBob on March 15, 2020, 04:52:18 PM

Title: If Fluorine is an electron withdrawing group, why is it an Ortho_Para director?
Post by: JoeyBob on March 15, 2020, 04:52:18 PM
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?
Title: Re: If Fluorine is an electron withdrawing group, why is it an Ortho_Para director?
Post by: chenbeier on March 15, 2020, 05:07:53 PM
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
Title: Re: If Fluorine is an electron withdrawing group, why is it an Ortho_Para director?
Post by: hollytara on March 15, 2020, 05:35:05 PM
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. 
Title: Re: If Fluorine is an electron withdrawing group, why is it an Ortho_Para director?
Post by: JoeyBob on March 15, 2020, 05:40:45 PM
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.