Goc acid strength
So, my teacher said hydrogen bonding will take place after i make conjugate base which makes it stable so it becomes a strong acid... Why can't hydrogen bond take place before making conjugate base, making it difficult to remove hydrogen and making it a bad acid?
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@Dexter
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That's a really good question.
Check the members in the chelate rings formed in both the cases. Which one would be favourable? If you get this, then there's your answer.
I don't get it....
What's a chelate ring?
If ur referring to coordination compds, it hasn't started in my coaching yet
probably because COO grps internal reso?
What do you mean by H bonding before making the base? Are we expecting the H from COOH to be attracted to the O electrons? If so, then check the pKa values:
benzoic acid: 4.19
Ortho hydroxy benzoic acid: 2.98 (the H from COOH breaks away easily, formin the COO- ion ie)
As soon as you put this in water it wants to give away H+ ions, hence it forms the more stable anion. The H from OH is also acidic (pKa 10) BUT it is less acidic than the benzoic acid one.
About chelation, yea it comes in coordination.
Hm thanks i get it now
Also I've wanted to know this for a while, if there the multiple acidic hydrogen, how do u determine the most acidic one without pka values?
Just take any general case, not specifically this question
i would say seeing the atoms its bonded to, the more electronegative the atom is the better the polarisability of the bond,facilitating better leaving of H+. the other major factors would include best possible resonating structures after removal of H+, and some other factors (H-bonding ofc) 😄 .
Chelate Ring is a ring structure being formed by some sort of attraction with the molecule like H Bonding
In our case, if the hydrogen bonding occurs the way you show, then it would give a 4 membered chelate ring which is highly strained (All atoms as sp3 but the angle is somehow around 90°).
But if the C=O makes a hydrogen bond with the
—OH then that would give us a 6 membered chelate.
And this is not really strained.
And in the second case, the acidity of the —OH decreases because of H Bonding which was already pretty less acidic but doesn't affect the —COOH.
I think you'll get my point of view now
But still he knows about ring strain and all if he has studied Isomerism and all.
We got to know that terminology in chemical bonding somehow 😀
It isn't really practical
You always need pka values when there are multiple acidic hydrogens.
But you can predict the same qualitatively in most cases by observing Resonance Structures and all.
Yeah i also guessed angle strain is reason
Alright
Thanks
Most Welcome
You can close the question now if that's clear
Yes you're right
+solved @Varun_Arora
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