Question

Ambident nucleophile is/are (A) \(\stackrel{\ominus}{\mathrm{CN}}\) (B) \(\stackrel{\ominus}{\mathrm{NO}}_{2}\) (C) (D) \(\stackrel{\ominus}{\mathrm{NO}}_{3}\)

Short answer

The ambident nucleophiles among the given options are: (A) \( \stackrel{\ominus}{\mathrm{CN}} \) and (B) \( \stackrel{\ominus}{\mathrm{NO}}_{2} \).

Step-by-step solution

Identifying ambident nucleophiles

To identify ambident nucleophiles, we need to look for ions with multiple potential nucleophilic sites. That means we need to examine each case and see if two different atoms in the ion can donate a lone pair of electrons. Let's examine each option.

Option (A): \( \stackrel{\ominus}{\mathrm{CN}} \)

The cyanide ion, \( \stackrel{\ominus}{\mathrm{CN}} \), has a carbon atom and a nitrogen atom, both bearing a lone pair of electrons. The negatively charged nitrogen serves as one site for nucleophilic attack, while the carbon atom with a lone pair forms another nucleophilic site. Therefore, cyanide is an ambident nucleophile.

Option (B): \( \stackrel{\ominus}{\mathrm{NO}}_{2} \)

The nitrite ion, \( \stackrel{\ominus}{\mathrm{NO}}_{2} \), has a central nitrogen atom connected to two oxygen atoms. Both oxygen atoms have lone pairs of electrons and are potential nucleophilic sites. Therefore, nitrite is also an ambident nucleophile.

Option (C): No option provided

There is no ion provided in option (C). Therefore, we cannot determine if it is an ambident nucleophile. Please verify the question and provide a proper ion if necessary.

Option (D): \( \stackrel{\ominus}{\mathrm{NO}}_{3} \)

The nitrate ion, \( \stackrel{\ominus}{\mathrm{NO}}_{3}, \) has one negatively charged oxygen atom, but this oxygen atom is resonance-stabilized with the other two oxygen atoms. Nitrate ion cannot act as an ambident nucleophile since there aren't two separate centers for nucleophilic attack; the only oxygen with a negative charge is engaged in resonance with the rest of the ion.

Conclusion

From the given options, the ambident nucleophiles are: (A) \( \stackrel{\ominus}{\mathrm{CN}} \) and (B) \( \stackrel{\ominus}{\mathrm{NO}}_{2} \).

Key concepts

Nucleophilic Sites

Nucleophilic sites are areas within a molecule that can donate electron pairs to form new bonds with other chemical species. These regions are crucial because they determine how a molecule can interact within a chemical reaction.

• An ambident nucleophile has more than one nucleophilic site, allowing it to interact in multiple ways.
• This leads to different possible reaction outcomes, as the molecule can attack at different points.

In the case of cyanide \(\stackrel{\ominus}{\mathrm{CN}}\), both carbon and nitrogen atoms can serve as nucleophilic sites due to their lone pairs of electrons. Similarly, in the nitrite ion \(\stackrel{\ominus}{\mathrm{NO}}_{2}\), two oxygen atoms offer potential nucleophilic sites. The presence of multiple nucleophilic sites in these ions is what classifies them as ambident nucleophiles. This feature is significant in chemistry, as it influences how these nucleophiles are used in synthetic transformations.

Lone Pair Electrons

Lone pair electrons are non-bonded electrons situated on an atom, allowing it to form dative or coordinate bonds during reactions. These electrons are crucial because they often dictate an atom's reactivity in a compound.

• Lone pairs are generally found in outer electron shells and are flexible in participating in chemical bonds.
• Lone pairs contribute to the nucleophilic character of a molecule, making them central to the formation of new chemical bonds.

In cyanide \(\stackrel{\ominus}{\mathrm{CN}}\), the carbon and nitrogen atoms each have lone pairs, enhancing their ability to donate electrons. Likewise, in nitrite \(\stackrel{\ominus}{\mathrm{NO}}_{2}\), the oxygen atoms use their lone pairs for potential reactions, promoting multiple pathways during chemical interaction. Recognition of lone pair locations aids in predicting reaction mechanisms and outcomes.

Resonance Stabilization

Resonance stabilization refers to the distribution of electron density across different atoms in a molecule, which stabilizes the molecule by delocalizing its charge. This concept is crucial for understanding why certain ions do not serve as ambident nucleophiles.

• Resonance involves the shifting of electrons in pi bonds or lone pairs, making a structure more stable.
• It typically results in equal distribution of electron density, reducing reactivity at specific sites.

For instance, the nitrate ion \(\stackrel{\ominus}{\mathrm{NO}}_{3}\) uses resonance to stabilize its negative charge across the entire structure, involving all three oxygen atoms. Because of this even distribution, there aren't distinct nucleophilic centers available, limiting nitrate to assign its nucleophilic activity primarily through resonance-delocalized sites. Understanding resonance is key to appreciating why some ions are not ambident nucleophiles, as the charge stabilizes, rather than concentrating at one site.