Key Principles

In $\beta$-keto esters, what is associated with considerable acidity - why?

The $\alpha$-hydrogen between both carbonyl groups. Because there is considerable ``pull" from the electronegative carbonyl oxygens, the $\alpha$-hydrogen ``comes" off easily:

Figure 49.5: Acidity of $\alpha$-hydrogen in keto esters: The $\alpha$-hydrogen has a p $K_{a} \approx 10$.

What type of rearrangement leads to the keto form?

Keto-enol tautomerism.

This process adds water to an alkyne creating a very unstable vinylic alcohol which then rearranges (or tautomerizes) to a ketone:

Figure 49.6: Keto-enol tautomerism.