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Chemistry Forums for Students => Organic Chemistry Forum => Topic started by: sharbeldam on February 05, 2020, 03:10:07 AM

Title: Hydrogen bonding or I effect?
Post by: sharbeldam on February 05, 2020, 03:10:07 AM
As much as I love organic chemistry, I dont think it loves me back (Flashback to every girl I've loved) because it always seem to put me in a difficult position with my students that i tutor and I just stare at the question without an answer.

If I'm comparing the acidity of ortho nitrophenol with para nitrophenol, I know that para is more acidic because it has resonance+I effect (ortho too) but ortho-nitrophenol has hydrogen bonding that reduces its acidity and hence ortho is less acidic -> that means that in this case Hydrogen bonding effect> I effect (Since NO2 is closer and withdraws electron more and should stabilize the conjugate base more.)


If I compare ortho flurophenol with para-fluorophenol, same logic but ortho is more acidic because I effect here is stronger than the hydrogen bonding effect.

Is there a rule to know when hydrogen bonding effect is stronger effect than I effect? if the atom is very electronegative like F, the I effect should be stronger, but so does the hydrogen bonding...

I really appreciate the *delete me* thanks.
Title: Re: Hydrogen bonding or I effect?
Post by: rolnor on February 05, 2020, 04:24:11 AM
Is there hydrogenbonding in o-fluorophenol? I think not.
Title: Re: Hydrogen bonding or I effect?
Post by: sharbeldam on February 05, 2020, 04:33:55 AM
Why not? The hydrogen that is connected to phenol oxygen with electron pair on F?
Title: Re: Hydrogen bonding or I effect?
Post by: AWK on February 05, 2020, 05:05:05 AM
In crystals, 2-fluorophenol forms hydrogen bonds only between phenolic groups.
Title: Re: Hydrogen bonding or I effect?
Post by: sharbeldam on February 05, 2020, 05:08:00 AM
This is not true then? Why?
Title: Re: Hydrogen bonding or I effect?
Post by: AWK on February 05, 2020, 05:13:14 AM
https://onlinelibrary.wiley.com/doi/10.1002/chem.19970030115
Title: Re: Hydrogen bonding or I effect?
Post by: sharbeldam on February 05, 2020, 05:28:27 AM
Everything I have been taught in the past apparently has been a lie.

Appreciate the help.
Title: Re: Hydrogen bonding or I effect?
Post by: AWK on February 05, 2020, 06:16:56 AM
Fluoride anion forms very strong hydrogen bonds