question about ranking bases

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Ok I was following the CARDIO rule from chad and was able to eliminate choice a and b. However when I came down to the last two choices (pyridine and piperidine) I am a bit confused.

So they both have neutral charge, same atom where electron lie, and no resonance in both.

But when it comes to dipole induction, don't the piperidine has one hydrogen bonded to the N and the pyrimidine has no hydrogen bonded to the N? Should I account for that as something pulling the electron or does the dipole induction only apply for electronegative atom like N,F, and O?

also let say there is no difference in dipole induction then the next thing to look at is orbital.

I tried drawing the structures while showing the lone pair but I am not sure about the structure of pyridine. Which one of the pyridine is correct?
the answer key said it has an sp2 hybridization so I assume it is the one on the left that is correct? but why can't I draw it like the one on the right? Should I just memorize the structures?


Also, am I supposed to know all of the exceptions to the rule? damn this sucks if the exceptions ones show up on the DAT
thanks




DRAWING

 

[premac]

Pyridine is the one on the left. That's just how it is.
Dipole induction only accounts for electronegative atoms.

 

[SN1]

Pyridine is the one on the left. That's just how it is.
Dipole induction only accounts for electronegative atoms.

thanks man. But I encountered another question where I needed to rank acids so I drew their conjugate bases.

again when comparing the phenoxide and carboxylate. I thought of phenoxide as being more stable because it has more resonance and therefore the weaker base and stronger acid. But the solution said carboxylate is more stable because the electrons are shared between two oxygen. WTH???? How many of these exceptions are there?
If I can't even compare those two correctly I would have gotten the answer wrong because the other two answers only have one other resonance structure.

DRAWING

 

[premac]

Yeah... Very tricky if you don't know the exceptions.
I remember Chad emphasizing exceptions couple times.
It should be a common sense that carboxylic acid is more acidic than phenol.
But, if you want to know the actual reason, I'll try to explain it.
You have to think about how resonance works. Electrons are EQUALLY delocalized between the two oxygen atoms in carboxylate. Thus, base form is very stable.
Now, in phenoxide, we see a lot more possible resonance structures. At a first glance, we would think that this would be more stable than carboxylate.
However, we should note that electrons in phenoxide are NOT EQUALLY delocalized. This is because oxygen is more electronegative than carbon. Bond between C-C isn't the same as C-O. So, the resonance of phenoxide structure is "disrupted" relative to the carboxylate structure.
This means that phenoxide is less stable, meaning that it's stronger base, thus weaker acid.

I hope that's not too confusing!

 

[Kratoz24x]

Would the most stable carboxylate be the one with most surface area?

 

[SN1]

Yeah... Very tricky if you don't know the exceptions.
I remember Chad emphasizing exceptions couple times.
It should be a common sense that carboxylic acid is more acidic than phenol.
But, if you want to know the actual reason, I'll try to explain it.
You have to think about how resonance works. Electrons are EQUALLY delocalized between the two oxygen atoms in carboxylate. Thus, base form is very stable.
Now, in phenoxide, we see a lot more possible resonance structures. At a first glance, we would think that this would be more stable than carboxylate.
However, we should note that electrons in phenoxide are NOT EQUALLY delocalized. This is because oxygen is more electronegative than carbon. Bond between C-C isn't the same as C-O. So, the resonance of phenoxide structure is "disrupted" relative to the carboxylate structure.
This means that phenoxide is less stable, meaning that it's stronger base, thus weaker acid.

I hope that's not too confusing!

Thanks for the explanation. But when you say "it should be common sense that carboxylic acid is stronger than phenol" uhhh how do you know that without knowing the ka or pka value?

what about acetic acid and carboxylic acid, how would you know which is stronger without their ka values?

 

[SN1]

Would the most stable carboxylate be the one with most surface area?

I think so. The bigger the atom, the more stable it is.

 

[premac]

Thanks for the explanation. But when you say "it should be common sense that carboxylic acid is stronger than phenol" uhhh how do you know that without knowing the ka or pka value?

what about acetic acid and carboxylic acid, how would you know which is stronger without their ka values?

It's common sense just because it's a common knowledge. It's just widely known, haha.

If you didn't know, acetic acid is a form of carboxylic acid. Carboxylic acid has R group attached to it, and that R group is CH3 in acetic acid.

 

[SN1]

It's common sense just because it's a common knowledge. It's just widely known, haha.

If you didn't know, acetic acid is a form of carboxylic acid. Carboxylic acid has R group attached to it, and that R group is CH3 in acetic acid.

LOL ok. I guess I forgot most of what I learned in orgo 1.5 years ago.