When asked to explain ‘What is a nucleophile?’, it is common to see an answer like –
A nucleophile is an atom, ion, or molecule that donates an electron pair to another molecule (usually an electron-deficient- electrophile) to form a chemical bond.
There are two ghastly mistakes in understanding the concept here -
1) A nucleophile is an atom, ion, or molecule that donates an electron pair to another molecule…
Electron pairs cannot be distributed based on demand.
Nucleophile is a specific term restricted to only those species that are inherently electron-rich, like molecules containing lone pair (for example, NH3 or H2O), negatively charged monoatomic or polyatomic ions (namely Cl-, OH-, AlH4-), or molecules containing a pie bond (as a benzene ring).
I still haven’t come across any electron-rich atom. An atom always has an equal number of electrons and protons to be electrically neutral. An atom that has gained an electron is still an atom but is called anion. So, using atom and ion together in a sentence to represent a nucleophile is incorrect.
Related Reading- Are ions a type of atom?
Also, nucleophiles don’t usually but always donate to the electrophiles.
2) The second mistake is assuming a nucleophile will form a chemical bond.
You must know that a chemical bond can be ionic or covalent in nature. If an electron-rich ion forms an ionic bond with an electron-deficient counterpart, the bond formation is due to electrostatic attraction. The term nucleophile is restricted to only those species that can donate their electrons to an electron-deficient counterpart and form a covalent bond.
So, we can redo the definition of a nucleophile as-
A nucleophile is an electron-rich species that can be negatively charged or neutral with an available pair of electrons which it donates to an electrophile and forms a covalent bond.
Related Reading – Definition of Nucleophile
The nucleophiles are categorized as – lone pair (neutral and charged), pie bond, and sigma bond based on the type of electrons participating in chemical reactions.
The most common nucleophilic atoms in organic chemistry are Oxygen, Nitrogen, and Sulphur. Their involvement forms common functional groups of alcohols, phenols, amines, thiols, and carboxylic acid derivates.
The other nucleophiles are - halogen as halides (X-), hydrogen anion as hydrides (H-), and Carbon nucleophiles (CN-, RMgX, R2CuLi, RLi, etc.)
Read More about the Nucleophiles in chemistry.
An organic reaction has several participants, and nucleophile is one of them. The chapter ‘Fundamentals of an Organic Reaction’ covers exhaustively all the components that drive a chemical reaction.
Enroll Now - Introductory Organic Chemistry