Nucleophiles are electron-rich species that can donate a pair of electrons and form a new covalent bond with an electron-deficient counterpart called the electrophiles. That is why electrophiles are referred to as lovers of electrons.
The nucleophiles donate electrons as lone pairs, pie bonds, or sigma bonds.
Read- What are nucleophiles?
The pie electrons are an easier electron source for a nucleophile because they are loosely held, unlike the sigma bond electrons. So, the way the pie bonds are formed (by the sideways orbitals overlap) contributes greatly to the labile nature of the electrons.
Read- How are covalent bonds formed? (Types of covalent bonds according to the Valence bond Theory)
The pie electrons of an alkene can break to accommodate two new sigma bonds by undergoing an electrophile addition reaction. The pie electrons of the aromatic ring can be more resilient. They can add an electrophile by substituting a proton (H+) and still retain the benzene ring’s aromaticity.
Read- Types of reactions a nucleophile can undergo.
Therefore, double bonds, triple bonds, or aromatic systems can participate in organic reactions as nucleophiles.
Related Reading- Techniques to identify a nucleophile – Visual Inspection Method - Part 1
Techniques to identify a nucleophile in organic reactions – Following the Arrow Trail
Nucleophiles are an important agent driving organic reactions. They are covered separately in the chapter ‘Fundamentals of Organic Reactions’ part of the Introductory Organic Chemistry course, a precursor guide to organic chemistry reactions covering over 500+ essential concepts.