Question

What are ambident nucleophiles?

Answer 1

Nucleophiles are the chemical species that donates an electron pair to form a chemical bond with the electrophile. As the name suggests nucleophile means it attracts positive charge. As they can donate electrons, we can call them Lewis base by definition.

Complete step by step answer:
Nucleophile, in chemistry, is an atom of molecule that has an extra pair of electrons or has negative charge, and hence attracts positively charged species. They are therefore known as Lewis base. Some examples are halogen ions, like chloride ion $C{l^ - }$ , bromide ion $B{r^ - }$, the hydroxide ion $O{H^ - }$, the cyanide ion $C{N^ - }$, ammonia $N{H_3}$ and water ${H_2}O$
So in question, we have an Ambident nucleophile. The word ambident comes from Latin words; ambi= on both sides, dens= tooth. So an ambident nucleophile has teeth on two sides and nucleophile means that seek positive charge.
Now we can say that ambident nucleophiles are anionic nucleophiles whose negative charge is delocalized by resonance over two unlike atoms or two- like but non- equivalent atoms. They can attack from two different places and can form two different products in a reaction.
For example, thiocyanate ion $SC{N^ - }$, is a resonance hybrid like-
$^ - S - C \equiv N\overset {} \longleftrightarrow S = C = {N^ - }$
Here both sulphur and Nitrogen can act as nucleophiles. So the ${S_N}2$ reaction of an alkyl chloride with the thiocyanate ion leads to a mixture of alkyl thiocyanate and alkyl isothiocyanate. As-
$R - Cl + SC{N^ - } \to C{l^ - } + R - SCN + R - NCS$

Note: A common ambident nucleophile in organic is the enolate ion $C{H_3}COC{H_2}^ - \overset {} \longleftrightarrow C{H_3}C{O^ - }C{H_2}$ both the carbon and oxygen acts as nucleophiles. So when a reaction between enolate and methyl chloride occurs, it gives a mixture of ketone and enol ether.