Q22-2P - Organic Chemistry (Mcmurry)

Question

How many acidic Hydrogens does each of the molecules listed in Problem 22-1 have? Identify them.

Step-by-Step Solution

Answer

Answer of subpart (a):

You need to identify the acidic Hydrogens of Cyclopentanone.

Answer of subpart (b):

You need to identify the acidic Hydrogens of Methyl thioacetate.

Answer of subpart (c):

You need to identify the acidic Hydrogens of Ethyl acetate.

Answer of subpart (d):

You need to identify the acidic Hydrogens of Propanal

Answer of subpart (e):

You need to identify the acidic Hydrogens of Acetic acid.

Answer of subpart (f):

You need to identify the acidic Hydrogens of Phenylacetone.

Step 1: Structure of keto-enol form of Cyclopentanone

You can draw the keto-enol tautomers like this;

Step 2: No. of acidic Hydrogens

The keto form of Cyclopentanone has 4 acidic Hydrogens.

The enol form of Cyclopentanone has one acidic Hydrogen.

Step 3: Explanation of the acidic Hydrogens in keto enol tautomers

In the keto-form; the Hydrogens which are connected to the carbon adjacent to the carbonyl carbons are acidic in nature.

Here, the keto-form of Cyclopentanone has 4 Hydrogen atoms which are connected to the adjacent carbonyl carbon. Therefore, the keto-form of the Cyclopentanone has 4 acidic Hydrogens atoms.

In the enol-form; the Hydrogens which are connected directly to the oxygen atom are acidic in nature.

Here, the enol-form of Cyclopentanone has 1 Hydrogen atom which is connected directly to the oxygen atom. Therefore, the enol-form of the Cyclopentanone has 1 acidic Hydrogen atom.

Step 4: Conclusion

Hence, the keto-enol tautomer of Cyclopentanone has 4 and 1 acidic Hydrogen atoms respectively

Step 5: Structure of keto-enol form of Methyl thioacetate

You can draw the keto-enol tautomers like this;

Step 6: No. of acidic Hydrogens

The keto form of Methyl thioacetate has 3 acidic Hydrogens.

The enol form of Methyl thioacetate also has 3 acidic Hydrogens.

Step 7: Explanation of the acidic Hydrogens in keto-enol tautomers

In the keto-form; the Hydrogens which are connected to the carbon adjacent to the carbonyl carbons are acidic in nature.

Here, the keto-form of Methyl thioacetate has 3 Hydrogen atoms which are connected to the adjacent carbonyl carbon. Therefore, the keto-form of the Methyl thioacetate has 3 acidic Hydrogens atoms.

In the enol-form; the Hydrogens which are connected directly to the oxygen atom are acidic in nature.

Here, the enol-form of Methyl thioacetate has 1 Hydrogen atom which is connected directly to the oxygen atom. Again, the hydrogen atoms with the double bonded carbon atom also show acidic behavior. Therefore, the enol-form of the Methyl thioacetate has 3 acidic Hydrogen atoms.

Step 8: Conclusion

Hence, the keto-enol tautomer of Methyl thioacetate has 3 and 3 acidic Hydrogen atoms respectively.

 

Step 9: Structure of keto-enol form of Ethyl acetate

You can draw the keto-enol tautomers like this;

Step 10: No. of acidic Hydrogens

The keto form of Ethyl acetate has 3 acidic Hydrogens.

The enol form of Ethyl acetate has also 3 acidic Hydrogens.

Step 11: Explanation of the acidic Hydrogens in keto-enol tautomers

In the keto-form; the Hydrogens which are connected to the carbon adjacent to the carbonyl carbons are acidic in nature.

Here, the keto-form of Ethyl acetate has 3 Hydrogen atoms which are connected to the adjacent carbonyl carbon. Therefore, the keto-form of the Ethyl acetate has 3 acidic Hydrogens atoms.

In the enol-form; the Hydrogens which are connected directly to the oxygen atom are acidic in nature.

Here, the enol-form of Ethyl acetate has 1 Hydrogen atom which is connected directly to the oxygen atom. Again, the hydrogen atoms with the double bonded carbon atom also show acidic behavior. Therefore, the enol-form of the Ethyl acetate has 3 acidic Hydrogen atoms.

Step 12: Conclusion

Hence, the keto-enol tautomer of Ethyl acetate has 3 and 3 acidic Hydrogen atoms respectively.

 

Step 13: Structure of keto-enol form of Propanal

You can draw the keto-enol tautomers like this;

Step 14: No. of acidic Hydrogens

The keto form of Propanal has 2 acidic Hydrogens.

The enol form of Propanal also has 2 acidic Hydrogens

Step 15: Explanation of the acidic Hydrogens in keto-enol tautomers

In the keto-form; the Hydrogens which are connected to the carbon adjacent to the carbonyl carbons are acidic in nature.

Here, the keto-form of Propanal has 2 Hydrogen atoms which are connected to the adjacent carbonyl carbon. Therefore, the keto-form of the Ethyl acetate has 2 acidic Hydrogens atoms.

The hydrogen atom directly connect to the carbonyl carbon atom is not acidic in nature.

In the enol-form; the Hydrogens which are connected directly to the oxygen atom are acidic in nature.

Here, the enol-form of Propanal has 1 Hydrogen atom which is connected directly to the oxygen atom. Again, the hydrogen atom with the double bonded carbon atom also shows acidic behavior. Therefore, the enol-form of the Propanal also has 2 acidic Hydrogen atoms.

Step 16: Conclusion

Hence, the keto-enol tautomer of Propanal has 2 and 2 acidic Hydrogen atoms respectively.

Step 17: Structure of keto-enol form of Acetic acid

You can draw the keto enol tautomers like this;

Step 18: No. of acidic Hydrogens

The keto form of Acetic acid has 4 acidic Hydrogens.

The enol form of Acetic acid also has 4 acidic Hydrogens.

Step 19: Explanation of the acidic Hydrogens in keto-enol tautomers

In the keto-form; the Hydrogens which are connected to the carbon adjacent to the carbonyl carbons are acidic in nature.

Here, the keto-form of Acetic acid has 3 Hydrogen atoms which are connected to the adjacent carbonyl carbon. Again, the hydrogen atom which is connected directly to the oxygen atom also shows acidic behavior. Therefore, the keto-form of the Acetic acid has 4 acidic Hydrogens atoms.

Hence, the three hydrogen atoms are less acidic than that of the one hydrogen atom.

In the enol-form; the Hydrogens which are connected directly to the oxygen atom are acidic in nature.

Here, the enol-form of Acetic acidhas 2 Hydrogen atoms which are connected directly to the oxygen atom. Again, the hydrogen atoms with the double bonded carbon atom also show acidic behavior. Therefore, the enol-form of the Acetic acidalso has 4 acidic Hydrogen atoms.

Hence, the enolic Hydrogens are less acidic than that of the carboxylic Hydrogens in the keto-form.

Step 20: Conclusion

Hence, the keto-enol tautomer of Acetic acid has 4 and 4 acidic Hydrogen atoms respectively.

 

Step 21: Structure of keto-enol form of Phenylacetone

You can draw the keto-enol tautomers like this;

Step 22: No. of acidic Hydrogens

The keto form of Phenylacetone has 5 acidic Hydrogens.

The enol form of Phenylacetone has one acidic Hydrogen.

Step 23: Explanation of the acidic Hydrogens in keto enol tautomers

In the keto-form; the Hydrogens which are connected to the carbon adjacent to the carbonyl carbons are acidic in nature.

Here, the keto-form of Phenylacetone has 5 Hydrogen atoms which are connected to the adjacent carbonyl carbon. Therefore, the keto-form of the Phenylacetone has 5 acidic Hydrogens atoms.

In the enol-form; the Hydrogens which are connected directly to the oxygen atom are acidic in nature.

Here, the two different enol-forms of Phenylacetone have 1 Hydrogen atom which is connected directly to the oxygen atom. Therefore, the enol-form of the Phenylacetone has 1 acidic Hydrogen atom.

Step 24: Conclusion

Hence, the keto-enol tautomer of Phenylacetone has 5 and 1 acidic Hydrogen atoms respectively.