20P - Organic Chemistry (Mcmurry)

Question

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

 

Step-by-Step Solution

Answer

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

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

Step 2: Mechanism of the reaction

Step 3: 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. 

Step 4: Conclusion

The full reaction is

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

Step 6: Mechanism of the reaction

Step 7: 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. 

 

Step 8: Conclusion

The full reaction is

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

Step 10: Mechanism of the reaction

Step 11: 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.

 

 

Step 12: Conclusion

The full reaction is

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

Step 14: Mechanism of the reaction

Step 15: 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.

 

Step 16: Conclusion

The full reaction is