[Lonn]

Which proton is more acidic? I though the blue one was more acidic because the charge is delocalized but in my book it says the red one is more acidic, can anyone tell me why.

[enahs]

What is the hybridization of the carbon atoms they are attached to?

[Lonn]

red H's carbon is sp3
blue H's carbon is sp2 which is supposed to make it even more stable/acid!

they have the same atoms, the blue proton's charge is delocalized which makes it more stable/acid, plus it's carbon has an sp2 hybridization state which also makes it more stable/acid. The only way I see the other proton could be more stable/acidic is by induction, if this is the case can you please tell me why, I really want to understand this.

[stevet]

the blue proton's charge is delocalized which makes it more stable/acid

Can you show how you would delocalise the charge if the blue proton was abstracted by a base?
Can you do the same for the red proton?

[Lonn]

I finally see that actually it is in the red proton's position that the negative formal charge is delocalized

I was thinking it was the other way around because I saw the drawing as if it had two methyl groups(where the protons are).

thanks for the help I feel a lot better with that cleared up!

[g-bones]

There is an even more pressing issue at hand here.  If you compare the acidity of the red proton with another proton that can be delocalized in an acyclic system, the acidity of the 5-membered ring is MUCH more acidic (pKa = 15)! Can you imagine a reason why this cyclic system would have such a stable anion?  (Hint: it may help to draw out the conjugate base and really look at the relationship of all of the electrons)