Chapter 19, Problem 19.13P

Interpretation Introduction

(a)

Interpretation:

The validation corresponding to the fact that aspartame is chiral is to be stated. If aspartame is chiral, then the possible number of stereoisomers for aspartame is to be stated.

Concept Introduction:

A compound that contains a chiral carbon is known as chiral compound. Carbon atom that contains all the four different atoms or group of atoms attached to it is referred as the chiral atom. This carbon is also known as stereocenter.

The possible number of stereoisomers is calculated by the expression $2^n$ in which $n$ corresponds to the number of stereocenters.

Answer to Problem 19.13P

Aspartame is a chiral compound. The possible number of stereoisomers for aspartame is $4$.

Explanation of Solution

The aspartame is a chiral compound. The structure of aspartame which contains chiral carbon atoms is shown as,

There are two chiral carbon atoms present in aspartame which are marked with asterisk sign. In the structure of aspartame, one carbon atom is directly bonded to ${\text{CH}}_{\text{2}}{\text{C}}_{\text{6}}{\text{H}}_{\text{5}}$, $\text{C}=\text{O}$ and ${\text{NH}}_{\text{2}}$ groups. The other carbon atom is bonded to ${\text{NH}}_3^{+}$, ${\text{CH}}_{\text{2}}$ and $\text{C}=\text{O}$ groups.

Thus, the possible number of stereoisomers in aspartame is,

$\begin{array}{c}\text{Number}\text{of}\text{stereoisomers}=2^n\\ =2^2\\ =4\end{array}$.

Where, $n$

• is the number of stereocenter.

Thus, the possible stereoisomers of aspartame is $4$.

Interpretation Introduction

(b)

Interpretation:

The name of each functional group present in aspartame is to be stated.

Concept Introduction:

An atom or a group of atoms that shows characteristic physical and chemical properties are collectively known as functional groups. The functional group is the most reactive part present in the molecule. The main functional groups are $\text{OH}$ (alcoholic group), ${\text{-NH}}_{\text{2}}$ (amine group), $\text{COOH(carboxylic}\text{group)}$, $\text{CHO}\left(\text{aldehydic}\text{group}\right)$ and $\text{C=O}\left(\text{ketonic}\text{group}\right)$.

Answer to Problem 19.13P

The name of each functional group present in aspartame is ester group $\left(-{\text{COCH}}_{\text{3}}\right)$, amide group $\left(-\text{CONH}\right)$, primary ammonium ion $\left({\text{NH}}_3^{+}\right)$ and carboxylate ion $\left(-{\text{COO}}^{-}\right)$.

Explanation of Solution

According to the structure of aspartame shown in Figure 1, there are four functional groups present in the structure of aspartame.

The name of all the functional group of aspartame is ester group $\left(-{\text{COCH}}_{\text{3}}\right)$, amide group $\left(-\text{CONH}\right)$, primary ammonium ion $\left({\text{NH}}_3^{+}\right)$ and carboxylate ion $\left(-{\text{COO}}^{-}\right)$.

Interpretation Introduction

(c)

Interpretation:

The net charge on aspartame molecule in an aqueous solution at $\text{pH}$.

$7.0$ is to be stated.

Concept Introduction:

The negative logarithm of hydrogen ion concentration of the solution is known as $\text{pH}$ of the solution. The neutral solution has $\text{pH}$ value equals to $7$. The $\text{pH}$ of acidic solution is less than $7$ and for basic solution, $\text{pH}$ value is more than $7$.

Answer to Problem 19.13P

The net charge on aspartame molecule in an aqueous solution at $\text{pH}$.

$7.0$ is $0$.

Explanation of Solution

In an aqueous solution of $\text{pH}$.

$7.0$, the carboxylic acid group gets deprotonated and forms a carboxylate ion and amine group obtain that proton from the carboxylic acid to form a ammonium ion.

Hence, there is no change of charge takes place in aspartame and it possesses zero net charge.

Interpretation Introduction

(d)

Interpretation:

The validation corresponding to the fact that aspartame is whether soluble in water or not is to be stated.

Concept Introduction:

According to the concept of solubility, it is mentioned that like dissolves like. Generally, polar compound can only be dissolved in polar solvents and non-polar or weakly polar compounds can only be dissolved in non-polar solvents or weakly polar solvents.

Answer to Problem 19.13P

Aspartame is soluble in water.

Explanation of Solution

The given structure of asparatame is present in zwitterion form which suggests that it is a polar molecule. According to the concept of like dissolves like, aspartame is soluble in water because water is also a polar molecule.

Interpretation Introduction

(e)

Interpretation:

The structural formulas for the products that are obtained by the complete hydrolysis of aspartame in aqueous $\text{HCl}$ are to be shown. The ionized structure of each product in the solution is to be shown.

Concept Introduction:

An atom or a group of atoms that shows characteristic physical and chemical properties are collectively known as functional groups. The functional group is the most reactive part present in the molecule. The main functional groups are $\text{OH}$ (alcoholic group), ${\text{-NH}}_{\text{2}}$ (amine group), $\text{COOH(carboxylic}\text{group)}$, $\text{CHO}\left(\text{aldehydic}\text{group}\right)$ and $\text{C=O}\left(\text{ketonic}\text{group}\right)$.

The addition of water molecule to the compound is known as hydrolysis that compound.

Answer to Problem 19.13P

The structural formulas for the products that are obtained by the complete hydrolysis of aspartame in aqueous $\text{HCl}$ are,

Explanation of Solution

The hydrolysis of aspartame in the presence of aqueous $\text{HCl}$ is shown as,

Figure 2.

The reaction of aspartame with aqueous $\text{HCl}$ results in the formation of methanol, carboxylic acids and dicarboxylic acid. In this reaction, $\text{HCl}$ protonates the amine group to form ammonium ion. The ionized ammonium ion is present in both the acidic products.

Interpretation Introduction

(f)

Interpretation:

The structural formulas for the products that are obtained by the complete hydrolysis of aspartame in aqueous $\text{NaOH}$ are to be shown. The ionized structure of each product in the solution is to be shown.

Concept Introduction:

An atom or a group of atoms that shows characteristic physical and chemical properties are collectively known as functional groups. The functional group is the most reactive part present in the molecule. The main functional groups are $\text{OH}$ (alcoholic group), ${\text{-NH}}_{\text{2}}$ (amine group), $\text{COOH(carboxylic}\text{group)}$, $\text{CHO}\left(\text{aldehydic}\text{group}\right)$ and $\text{C=O}\left(\text{ketonic}\text{group}\right)$.

The addition of water molecule to the compound is known as hydrolysis that compound.

Answer to Problem 19.13P

The structural formulas for the products that are obtained by the complete hydrolysis of aspartame in aqueous $\text{NaOH}$ are,

Explanation of Solution

The hydrolysis of aspartame in the presence of aqueous $\text{NaOH}$ is shown as,

Figure 3.

The reaction of aspartame with aqueous $\text{NaOH}$ results in the formation of methanol, carboxylate ion and dicarboxylate ion. In this reaction, base abstracts the proton from carboxylic acid group to form carboxylate ions.