52 Replies
@Dexter
Note for OP
+solved @user1 @user2... to close the thread when your doubt is solved. Mention the users who helped you solve the doubt. This will be added to their stats.Resonance stabilized
So 2 is more stable
how does that correlate to acidic strength , for acidity order wont we check the stability of carbanion
what is the complete ans given ?
i dont quite understand it well , arnt the alpha hydrogen of the neigboring carbon
3 I think. First take the conjugate base by abstracting proton. In both, resonance is present, but, in 2, there is cross conjugation, so the carbanion is not as stable. 3 has more stable conjugate base, hence, more acidic.
i understand the order but i wanted to know which will be more acidic btw 2 and 3 and wdym by cross conjugation
That's what I said. 3 will be more acidic since the conjugate base is more stable.
yes idk how to check conjugate base stability btw 3 and 2
By cross conjugation, I mean that the carbonyl group can have resonance from the left, and also the right, which means that it's withdrawing power is lessened for the carbanion.
So carbanion is stabilized less
what the the resonance options have to do with withdrawing power
also the 3rd one is symmetrical so talking abt left and right is meaningless unless they happen at once no?
There's no cross conjugation in the third one, correct. It doesn't apply at all to the third one, just the second one
wdym by left right resonance in 2 then
What i sent just above.
1 oxygen resonantes with other oxygen?
Electrons can shift from both the oxygen as well as carbanion.
Precisely.
And because of that, the double bonded oxygen is withdrawing less by resonance from the carbanion.
u mean smth like this ?
and other is that crabanion just resonantes
Yes.
why would this be even possible
this is just unstable
why will we create more charges
It's a resonating structure. All possibilities exist, in differing probabilities.
so conjugate base of 2 is more stable than 3 because it has more resonating structures?
It's less stable than that of 3
Because 3 has complete resonance stability, while in 2, carbanion is competing with the other oxygen
how , in 3 it only resonates with the carbonyl how will it resonate with that oxygen
I think you're getting something wrong here. Wait, I'll type out the entire thing.
In 2, the conjugate base has negative charge being pulled from it by carbonyl group. However, carbonyl group is also receiving electron density from the other oxygen. Hence, it's withdrawing effect is weaker than normal.
In 3, the conjugate base has its electron density withdrawn by carbonyl group, with full strength.
So, 3 has more stable conjugate base.
@Gamertug pls tell me what you don't understand
ok i understand this
but doesnt 2 has more resonating struc
and more struc = more stable
Doesn't matter if the resonance itself is weakened.
🗿
how do u know it wont matter here without knowing the ans
Just because it has more resonating structures doesn't mean it's more stable because if a single structure predominates over all the others, then the contribution of the other structures is nearly zero.
2 has 1 resonating structure 1 is decent and other is poor
3 has 1 resonating struct which doesnt seem too much stable compared to the one from 2
The issue is that none of them are true structures. Consider the hybrid. 2 has one major delocalised cloud, and one localised charge on carbanion, which gets pulled, yes, but not a lot. Also note that the delocalised and localised clouds are pretty close together.
3 also has one delocalised and one localised clouds but they're much further apart.
this has me confused i will come back to it later
oh yes wait
Understandable. Don't try to think too deep about it. Just take a break and look at it again after a while.
so what does sepration has to do with stability
Electrostatic repulsion.
oooooooooooh
ic
Coulombic potential still applies
yes
but my question is , in exam how will u decide which to pick
1 decent and 1 weak or 1 strong
without knowing proper values
It's honestly just a bet atp.
Just go with the most convenient logic/train of thought
If it's Mains, there's probably only going to be a single criterion on which a question depends rather than multiple
@Opt do u understand what he did here
Oh, no.of acidic protons
That's it.
nvm i understand it now too
The reason you wouldn't judge acidic strength based on no.of acidic protons is that the Ka2, 3 and so on are generally several orders of magnitude less than the Ka1, so in the end it really only matters on the first dissociation.
so that reason wont count?
It's negligible
+solved @Opt
Post locked and archived successfully!
Archived by
<@1035556259417571408> (1035556259417571408)
Time
<t:1742860067:R>
Solved by
<@763645886500175892> (763645886500175892)