Chapter 17, Problem 17.34P

Interpretation Introduction

(a)

Interpretation:

Among the given pair of compounds, which compound has the polar pi bond that will undergo nucleophilic addition more rapidly is to be identified and explained.

Concept introduction:

A Nucleophilic addition reaction involves a polar $\text{π}$ bond which has an atom that is relatively electron-poor (i.e electrophile), so it tends to undergo the addition of a nucleophile, which is electron-rich. The most common polar $\text{π}$ bond that participates in nucleophilic addition reactions is the one in the carbonyl $\left(\text{C = O}\right)$ group. The carbon atom in the carbonyl group is electron-deficient (carries a partial positive charge); thus, the electron-withdrawing groups attached to this carbon will increase the concentration of a partial positive charge and thus such a compound will undergo a nucleophilic addition reaction more rapidly. On the contrary, electron-donating groups attached to the carbonyl carbon will decrease the positive charge on it and thereby undergo a nucleophilic addition reaction slowly.

Answer to Problem 17.34P

Among the given pair of compounds, the second compound has the polar pi bond that will undergo nucleophilic addition more rapidly than the first one. This is because with fewer alkyl groups attached to the carbonyl carbon, there is less bulkiness and greater concentration of positive charge.

Explanation of Solution

The given pair of compounds are

The electron-donating groups attached to the carbonyl carbon will decrease the concentration of the positive charge on the carbonyl carbon atom. In the first compound, the carbonyl carbon has two electron-donating substituents attached. In the second compound, the carbonyl carbon has only one electron-donating substituent attached. The partial positive charge on the carbonyl carbon of the second compound is greater as compared to the first one. This makes the carbonyl carbon of the second compound more electrophilic, thus, it will have more polar pi bond. Due to this, it will undergo nucleophilic addition reactions more rapidly. Due to fewer alkyl groups attached in the second compound, there is less bulkiness and hence greater contribution of a positive charge.

Conclusion

Electron-donating groups directly attached to the carbonyl carbon will decrease the concentration of a partial positive charge and make the pi bond less polar.

Interpretation Introduction

(b)

Interpretation:

Among the given pair of compounds, which compound has the polar pi bond that will undergo nucleophilic addition more rapidly is to be identified and explained.

Concept introduction:

A Nucleophilic addition reaction involves a polar $\text{π}$ bond which has an atom that is relatively electron-poor (i.e electrophile), so it tends to undergo the addition of a nucleophile, which is electron-rich. The most common polar $\text{π}$ bond that participates in nucleophilic addition reactions is the one in the carbonyl $\left(\text{C = O}\right)$ group. The carbon atom in the carbonyl group is electron-deficient (carries a partial positive charge), thus, the electron-withdrawing groups attached to this carbon will increase the concentration of a partial positive charge and thus such a compound will undergo a nucleophilic addition reaction more rapidly. On the contrary, electron-donating groups attached to the carbonyl carbon will decrease the positive charge on it and thereby undergo a nucleophilic addition reaction slowly.

Answer to Problem 17.34P

Among the given pair of compounds, the second one has a more polar pi bond that will undergo nucleophilic addition more rapidly than the first one. This is because a substituent - ${\text{CF}}_3$ is an electron-withdrawing group whereas a ${\text{CH}}_3$ group is an electron-donating group. So, the ${\text{CF}}_3$ group induces a greater positive charge on the carbonyl carbon.

Explanation of Solution

The given pair of compounds are

The electron-withdrawing groups attached to the carbonyl carbon will increase the concentration of the positive charge on the carbonyl carbon atom. In the first compound, the carbonyl carbon has a benzene ring at one end, and a ${\text{CH}}_{\text{3}}$ group at the other. In the second compound, the carbonyl carbon has a benzene ring at one end, and a ${\text{CF}}_{\text{3}}$ group at the other. The bulkiness of both these substituents is nearly the same. However, ${\text{CF}}_3$ is an electron-withdrawing group, whereas ${\text{CH}}_3$ group is an electron-donating group. So, the ${\text{CF}}_3$ group induces a greater positive charge on the carbonyl carbon. The partial positive charge on the carbonyl carbon of the second compound is greater as compared to the first one. This makes the carbonyl carbon of the second compound more electrophilic, thus, it will have more polar pi bond. Due to this, it will undergo nucleophilic addition reactions more rapidly.

Conclusion

Electron-withdrawing groups directly attached to the carbonyl carbon will induce a greater concentration of a partial positive charge and make the pi bond more polar.

Interpretation Introduction

(c)

Interpretation:

Among the given pair of compounds, which compound has the polar pi bond that will undergo nucleophilic addition more rapidly is to be identified and explained.

Concept introduction:

A Nucleophilic addition reaction involves a polar $\text{π}$ bond which has an atom that is relatively electron-poor (i.e electrophile), so it tends to undergo the addition of a nucleophile, which is electron-rich. The most common polar $\text{π}$ bond that participates in nucleophilic addition reactions is the one in the carbonyl $\left(\text{C = O}\right)$ group. The carbon atom in the carbonyl group is electron-deficient (carries a partial positive charge), thus, the electron-withdrawing groups attached to this carbon will increase the concentration of a partial positive charge and thus such a compound will undergo a nucleophilic addition reaction more rapidly. On the contrary, electron-donating groups attached to the carbonyl carbon will decrease the positive charge on it and thereby undergo a nucleophilic addition reaction slowly.

The concentration of the positive charge on the carbonyl carbon increases as the distance between an electron-withdrawing atom or group and the carbonyl carbon decreases.

Answer to Problem 17.34P

Among the given pair of compounds, the first one has more polar pi bond that will undergo nucleophilic addition more rapidly than the second one. This is because with the chlorine atom closer to the carbonyl carbon, the carbonyl carbon will bear a greater concentration of positive charge.

Explanation of Solution

The given pair of compounds are

Among the given pair of compounds, the first one has more polar pi bond that will undergo nucleophilic addition more rapidly than the second one. This is because with the chlorine atom closer to the carbonyl carbon, the carbonyl carbon bears a greater concentration of positive charge. The partial positive charge on the carbonyl carbon of the first compound is greater as compared to the second one. This makes the carbonyl carbon of the first compound more electrophilic, thus, it will have more polar pi bond. Due to this, it will undergo nucleophilic addition reactions more rapidly.

Conclusion

The concentration of the positive charge on the carbonyl carbon increases as the distance between an electron-withdrawing atom or group and the carbonyl carbon decreases.

Interpretation Introduction

(d)

Interpretation:

Among the given pair of compounds, which compound has the polar pi bond that will undergo nucleophilic addition more rapidly is to be identified and explained.

Concept introduction:

A Nucleophilic addition reaction involves a polar $\text{π}$ bond which has an atom that is relatively electron-poor (i.e electrophile), so it tends to undergo the addition of a nucleophile, which is electron-rich. The most common polar $\text{π}$ bond that participates in nucleophilic addition reactions is the one in the carbonyl $\left(\text{C = O}\right)$ group. The carbon atom in the carbonyl group is electron-deficient (carries a partial positive charge), thus, the electron-withdrawing groups attached to this carbon will increase the concentration of a partial positive charge and thus such a compound will undergo a nucleophilic addition reaction more rapidly. On the contrary, electron-donating groups attached to the carbonyl carbon will decrease the positive charge on it and thereby undergo a nucleophilic addition reaction slowly.

Answer to Problem 17.34P

Among the given pair of compounds, the first one has more polar pi bond that will undergo nucleophilic addition more rapidly than the second one. This is because the nitrile carbon bears a higher concentration of positive charge owing to the presence of the electron-withdrawing ${\text{CCl}}_{\text{3}}$ group. The ${\text{CH}}_{\text{3}}$ group is electron-donating.

with the chlorine atom closer to the carbonyl carbon, the carbonyl carbon bears a greater concentration of positive charge. [DK1]

Explanation of Solution

The given pair of compounds are:

Among the given pair of compounds, the first one has more polar pi bond that will undergo nucleophilic addition more rapidly than the second one. This is because the nitrile carbon bears a higher concentration of positive charge owing to the presence of the electron-withdrawing ${\text{CCl}}_{\text{3}}$ group. The ${\text{CH}}_{\text{3}}$ group is electron-donating. This makes the nitrile carbon of the first compound more electrophilic, thus, it will have more polar pi bond. Due to this, it will undergo nucleophilic addition reactions more rapidly.

Conclusion

Electron-withdrawing groups directly attached to the pi bond will induce a greater concentration of a partial positive charge and makes the pi bond more polar.

[DK1]