What is nucleophile and what is nucleophilic substitution reaction?
Nucleophile is an electron rich species, nucleus loving, generally contain lone pair of electrons. Eg. OH-, NH2, RCOO-.Nucleophilic substitution reaction is the reaction where stronger nucleophile displaces a weaker nucleophile from the substrate molecule. The nuclophile which is weak and leaves the substrate molecule with the bond pair is called leaving group.