Question

For each reaction below, give the corresponding keto/enol tautomer and provide the complete mechanism.

Short answer

You need to provide the keto-enol tautomers and full mechanism for all the reactions.

Step-by-step solution

Answer of subpart (a): Step 1: The keto-enol tautomer 

Mechanism of the reaction

Explanation of the mechanism

First the double bond of the enol form got protonated by the acid and forms a carbocation;

Then the carbocation is deprotonated by water and forms the keto form.

Conclusion

The full reaction is

Answer of subpart (b): Step 5: The keto-enol tautomer

Mechanism of the reaction

Explanation of the mechanism 

First the oxygen of the keto form got protonated by the acid;

Then the hydrogen from α-carbon is abstracted by water and subsequently forms the double bond that is the enol form.

Conclusion 

The full reaction is

Answer of subpart (c): Step 9: The keto-enol tautomer

Mechanism of the reaction

Explanation of the mechanism 

First the hydrogen of -OH group of the enol form is abstracted by the base which forms a negative charge on the oxygen;

Then the negative charge participates in resonance with the double bond.

Then the negative charge abstracts a proton from water and becomes the keto form.

Conclusion 

The full reaction is

Answer of subpart (d): Step 13: The keto-enol tautomer

Mechanism of the reaction 

Explanation of the mechanism 

First the hydrogen of the α-carbon of the keto form is abstracted by the base which forms a negative charge;

Then the negative charge participates in resonance with the lone pairs of oxygen.

Then the oxygen abstracts a proton from water and becomes the enol form.

Conclusion 

The full reaction is