most acidic proton?

[Akeane]

Which is the most acidic proton in 2-methyl-2-cyclopenten-1-one, and why?

 

 

[hypervalent_iodine]

This is presumably a homework question, so what specifically don't you understand about it that's preventing you from being able to answer it?

[Akeane]

Thank you for your reply!

 

I understand that you need to look at the stability of the resulting conjugate base to determine which is the most acidic proton. To do this, you need to consider the type of atom the proton is attached to (the more electronegative, the better), whether there are resonance structures that can delocalize the charge, whether there is the possibility of induction, and finally, the type of orbital.

 

According to these criteria, I narrowed it down to the hydrogens attached to either C4 or C5 on the ring.I chose one attached to C5 because it is closest to the pi bond between the carbon and the oxygen, and the resulting negative charge could be delocalized by the oxygen. However, the answer key indicates that it should be a hydrogen attached to C4. I do see that the pi bond between two carbons in the ring can help to delocalize the negative charge, but I do not see why this trumps what I described earlier, especially since the oxygen is electronegative.

 

Any help in clarifying these concepts for me would be greatly appreciated!

[Horza2002]

Think about how many resonance structure you can draw for the C-4 and C-5 anions. How might this effect the stability?