Concept explainers
(a)
Interpretation:
The structure of diethyl malonate showing acidic hydrogens is to be stated. The reason as to why it is more acidic than ordinary ester is to be stated.
Concept introduction:
Acidic hydrogen is defined as hydrogen that carries positive charge when the acid dissociates. The acidity in esters depends upon the stability of enolate ion. The higher is the stability of enolate ion higher is the acidity.
Answer to Problem 22.1P
The structure of the diethyl malonate showing acidic hydrogens is given below.
The diethyl malonate is more acidic than ordinary ester because its conjugate base is stabilized by delocalization of negative charge as shown below.
Explanation of Solution
In diethyl malonate the methylene group is surrounded by two carbonyl groups as shown below.
Figure 1
This active hydrogen is abstracted by base and generates a negative charge. The negative charge is delocalized between carbon and oxygen. This delocalization stabilizes the enolate ion. However, the presence of two carbonyl group increases the polar effect and stabilize the enolate ion. The diethyl malonate is more acidic than ordinary ester as its conjugate base is stabilized by delocalization of negative charge.
The acidity of the carbonyl compound is directly proportional to the stability of the enolate ion. The conjugate base stabilized by delocalization of diethyl malonate is shown below.
Figure 2
The structure of the diethyl malonate showing acidic hydrogens is given in Figure 2. The diethyl malonate is more acidic than ordinary ester due to delocalization of negative charge in its conjugate base.
(b)
Interpretation:
The structure of ethyl acetoacetate showing acidic hydrogens is to be stated. The reason as to why it is more acidic than ordinary ester is to be stated.
Concept introduction:
Acidic hydrogen is defined as hydrogen carry positive charge when the acid dissociates. The acidity in esters depends upon the stability of enolate ion. The higher is the stability of enolate ion higher is the acidity.
Answer to Problem 22.1P
The structure of ethyl acetoacetate showing acidic hydrogens is given below.
The ethyl acetoacetate is more acidic than ordinary ester because its conjugate base is stabilized by delocalization of negative charge as shown below.
Explanation of Solution
In ethyl acetoacetate, the methylene group is surrounded by two carbonyl groups as shown below.
Figure 3
This active hydrogen is abstracted by base and generates a negative charge. The negative charge is delocalized between carbon and oxygen. This delocalization stabilizes the enolate ion. However, the presence of two carbonyl groups increases the polar effect and stabilize the enolate ions. The conjugate base stabilized by delocalization of ethyl acetoacetate is shown below.
Figure 4
The ethyl acetoacetate is more acidic than ordinary ester as its conjugate base is stabilized by delocalization of negative charge.
The structure of ethyl acetoacetate is shown in Figure 3 and the acidic character of ethyl acetoacetate is shown in Figure 4.
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Chapter 22 Solutions
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