Question

Which of the following is an electrophile?
A.${{\text{H}}_{\text{2}}}{\text{O}}$
B.${\text{S}}{{\text{O}}_{\text{3}}}$
C.${\text{N}}{{\text{H}}_{\text{3}}}$
D.${\text{ROR}}$

Answer 1

Hint: An electrophile is a chemical species which is electron deficient. They bond with electron rich nucleophiles. As they accept electrons, they are Lewis acids. Mostly they are positively charged. They interact using addition and substitution reactions. Ex – cation, carbenes, radicals etc.

Complete step by step answer:
As we know that, electrophiles are electron deficient, i.e. they have a partial positive charge or an atom which does not have a complete octet.
In option A, water contains an oxygen atom bonded with two hydrogen atoms. Being the electronegative atom, the electron density is concentrated on the oxygen atom and the hydrogen atoms have fully filled shells. Thus, water is a nucleophile.
In option B, sulphur trioxide contains a sulphur atom doubly bonded to three oxygen atoms. Oxygen being the electronegative atom will pull the electron density from sulphur. This will result in a partial positive charge over sulphur. Thus, sulphur trioxide is an electrophile.
In option C, ammonia contains nitrogen bonded with three hydrogen atoms along with a lone pair. Due to this lone pair, ammonia is electron rich and acts as a nucleophile.
In option D, ether consists of an oxygen atom bonded with two alkyl groups. The alkyl groups are neutral while oxygen has two lone pairs of electrons. This means that it is electron rich and thus is a nucleophile.

$\therefore $ The correct option is option B, i.e. ${\text{S}}{{\text{O}}_{\text{3}}}$ .

Note:
Electrophiles mostly react with nucleophiles. For example, sulphur dioxide reacts with water, a nucleophile to form sulphurous acid. The reaction goes as:
${\text{S}}{{\text{O}}_{\text{2}}}{\text{ + }}{{\text{H}}_{\text{2}}}{\text{O}} \to {{\text{H}}_{\text{2}}}{\text{S}}{{\text{O}}_{\text{3}}}$
Nucleophiles are mostly compounds with lone pairs of electrons or compounds having a complete octet.