What are ambident nucleophiles? Explain with an example.

Ambident nucleophiles are molecules or ions that have two distinct nucleophilic sites, or two different atoms or groups that can act as nucleophiles by donating a pair of electrons to form a chemical bond with an electrophilic center or atom. These nucleophiles can react in different ways depending on which of their nucleophilic sites is involved in the reaction. The term "ambident" comes from the Latin words "ambi," meaning "both," and "dent," meaning "tooth," indicating that these molecules have two "teeth" for nucleophilic attack.

A classic example of an ambident nucleophile is the cyanide ion (CN⁻). The cyanide ion consists of a carbon atom (C) and a nitrogen atom (N), and both of these atoms can act as nucleophiles. Let's explore two different reactions that demonstrate the ambident nucleophilic behavior of the cyanide ion:

Attack on an electrophilic carbon atom:
In this reaction, the carbon atom in the cyanide ion (C) acts as the nucleophilic site and attacks an electrophilic carbon atom in an organic compound, such as an alkyl halide (e.g., methyl iodide, CH₃I). The reaction can be represented as follows:

CN⁻ + CH₃I → CH₃CN + I⁻

Here, the carbon atom in the cyanide ion attacks the carbon atom in methyl iodide, leading to the formation of acetonitrile (CH₃CN) and iodide ion (I⁻).

Attack on an electrophilic nitrogen atom:
In another reaction, the nitrogen atom in the cyanide ion (N) can act as the nucleophilic site and attack an electrophilic carbon atom in a compound like isocyanides (RNC). The reaction can be represented as follows:

CN⁻ + RNC → RNC-CN

Here, the nitrogen atom in the cyanide ion attacks the carbon atom in the isocyanide molecule, forming a cyanide-terminated isocyanide compound.

In both reactions, the cyanide ion acts as a nucleophile, but it uses different nucleophilic sites (carbon or nitrogen) to form distinct products. This ambident nucleophilic behavior of CN⁻ illustrates the concept of having multiple nucleophilic centers within a single molecule or ion, allowing it to participate in diverse chemical reactions depending on the reaction conditions and the electrophilic species it encounters.