Question

How can I identify the nucleophile and the electrophile in the `AlCl_3 + NH_3 -> Cl_3Al^(-)NH_3^+` acid–base reaction?

Answer 1

To identify whether a compound is a nucleophile or an electrophile, you need to know what these two terms mean?

Let’s start with “nucleophiles” (from “nucleus loving”, or “positive-charge loving”). A nucleophile is a reactant that provides a pair of electrons to form a new covalent bond.

examples of nucleophiles are ammonia ( it has a lone pair of electron on its Nitrogen atom), negative ions like chloride, hydroxide ion, cyanide ion.

Now let’s talk about electrophiles (from “electron-loving”, or “negative-charge loving”). An electrophile is a species that accepts a pair of electrons to form a new covalent bond.
examples include Boron trifluoride, Aluminum chloride,Hydronium ion etc.

In Aluminum chloride the central Aluminum atom is in s`p^3` hybridized state . It has used one of its three half filled s`p^3` orbitals to form one covalent bond with three Chlorine atoms .It has still one vacant s`p^3` hybridized orbital which can accept a pair of electron from other species making Aluminum chloride an electrophile.