What is an ambident nucleophile?

Question

41074 views around the world

You can reuse this answer
Creative Commons License

Answer 1 · 2015-05-03T01:02:02

An ambident nucleophile is an anionic nucleophile in which the negative charge is delocalized over two unlike atoms.

A nucleophile is a chemical species that can donate an electron pair and form a bond to a carbon atom. For example,

www.naontiotami.com

The word ambident comes from two Latin words: ambi = "on both sides" + dens = "tooth".

So an ambident nucleophile has "teeth" on two sides.

It can attack from two different places and form two different products.

For example, the thiocyanate ion, $"SCN"^-$ , is a resonance hybrid.

www.axeleratio.com

Both the $"S"$ and the $"N"$ atoms can act as nucleophiles.

So, the $"S"_"N"2$ reaction of an alkyl halide with $"SCN"^−$ often leads to a mixture of an alkyl thiocyanate and an alkyl isothiocyanate.

$"R-X" + "SCN"⁻ → "X"^(-) + underbrace("R-SCN")_color(red)("alkyl thiocyanate") + underbrace("R-NCS")_color(red)("alkyl isothiocyanate")$

A common ambident nucleophile in organic chemistry is the enolate ion.

For example, the resonance forms of acetone enolate are

chem.libretexts.org

Both the $"C"$ and the $"O"$ atoms can act as nucleophiles.

Thus, the reaction of the enolate with methyl iodide gives a mixture of a ketone (1) and an enol ether (2).

www.thecatalyst.org