What are electrophiles and nucleophiles? Explain with examples.

(i) Electrophiles (Electrophilic reagents): Electrophiles are electron loving chemical species having an atom which is deficient in electrons. There are two types of electrophiles:
(a) Positively charged ions or positive electrophiles: These are deficient in electrons and carry a positive charge. For example H⁺ (hydrogen ion) 


 
etc.

(b) Neutral electrophiles. These are electrophilic reagents in which the electron deficient atom does not carry any charge. For example, AlCl₃, FeCl₃, BF₃, SnCl₄. Carbenes also act as electrophiles because the carbon in them has only six electrons.

Since both positively charged and neutral electrophiles are short by a pair of electrons, they have strong tendency to attract electrons from other sources and hence behave as Lewis acids.

Electrophiles always attack the substrate molecule at the point of high electron density.

(ii) Nucleophiles (or Nucleophilic reagents): Nucleophiles are nucleus loving chemical species containing an atom having an unshared or lone pair of electrons. Nucleophiles are two types:

(a) Negatively charged ions or Negative nucleophiles: These have excess electron pairs I and carry a negative charge. For example OH^– J (hydroxyl ion), X^– (halide ion), RO^– (alkoxide ion), CN^– (cyanide ion) and carbanions.

(b) Neutral nucleophiles: These are I nucleophilic reagents which contain atoms with lone pairs of electrons but do not carry any charge. For example, (water); 

 

(ethers) etc. 
Since both negatively charged and neutral nucleophiles contain at least one unshared pair of electrons, they have strong tendency to donate this pair of electrons to electron deficient species and hence behave as Lewis bases.