Before we delve into learning about electrophiles and nucleophiles lets us quickly recall what an attacking reagent is. The species that attacks a substrate molecule or intermediate and forms a product is called attacking reagent. It is of two types:
Electrophilic reagent or electrophiles
Nucleophilic reagent or nucleophiles
What is Electrophile?
The word electrophile is made from “electro” derived from electron and “phile” which means loving.
Any molecule, ion or atom that is deficient in electron in some manner can act as an electrophile. In other words, the reagent which attacks the negative of the molecule or loves electrons is called electrophile. They are generally positively charged or are neutral species (electron-deficient molecules) with empty orbitals. Electrophiles can accept a couple of electrons.
Types of Electrophiles
The different types of electrophiles can be classified as:
1. Positively Charged Electrophiles:
H+, SO3H+, NO+, NO2+, X+, R+ , C6H5N2+, C+2H-OH, CH3 C+ =O
2. Neutral Electrophiles: These showcase electron deficiency.
(a) All Lewis acids: BF3, AlCl3, SO3, ZnCl2, BeCl2, FeCl3, SnCl2, CO2, SnCl4.
(b) The neutral atom that accepts electrons from the substrates :
> *C = O, R *COCl, R – * Mg – X, *I – Cl, CH3 – *CN, R*–Cl, R*–O,
The star (*) indicates the atom that accepts electrons.
(c) Free radicals, carbenes and nitrene act as electrophiles.
(d) Species with electrophilic centre:
What is Nucleophile?
A nucleophile is a reactant which gives an electron pair to form a covalent bond. A nucleophile is usually charged negatively or is neutral with a lone couple of donatable electrons. H2O, -OMe or -OtBu are some examples. Overall, the electron-rich species is a nucleophile.
The word nucleophile is made from two words “Nucleo” derived from the nucleus and “phile” which means loving. Species that attacks the positive side of the substrate or loves nucleus are called nucleophiles.
Nucleophiles donate unshared electron pairs, and they act as Lewis bases, according to Lewis ‘notion of acids and bases.
Points to Remember:
- They consist of electrons and instead are attracted towards the nucleus. They are either negatively or neutrally charged.
- They are donors of electrons.
- Electrons move from low-density area to high-density area.
- They support nucleophilic addition and nucleophilic substitution reactions.
- Also called as Lewis base.
Types of Nucleophiles
The different types of nucleophiles can be classified as:
1. Negatively Charged Nucleophiles:
2. All Lewis base which contains lone pairs:
(iii)
The star (*) indicates the atom which donates electrons to the substrate.
4. Ambident Nucleophile:
Nucleophiles which have two sites of electron-rich centre or in which two or more atoms bear an unshared pair of electrons.
Example:
Resonating structures are also ambient nucleophiles.
5. Amphiphile Nucleophile: Molecule containing multiple bonds between carbon and a more electronegative atom can act both as electrophiles or nucleophiles.
For example:
Difference between Electrophile and Nucleophile
To make you understand how electrophile and nucleophile are different from each other, here are some major differences between them:
| ELECTROPHILE | NUCLEOPHILE |
| Accepts the electron pair | Supplies the electron pair |
| These can be either positively charged or neutral species | They can be either negatively charged or neutral species |
| Possess an empty orbital to receive the electron pair | Possess an electron pair which is loosely held and can be supplied easily |
| Attacks the points of high electron density | Attacks the point of low electron density |
| These are known as Lewis acid as they can accept a pair of electrons | These are known as Lewis base as they can donate a pair of electrons |
| Forms an extra bond with the nucleophile | Increases its covalency by one unit |
| Example: All positively charged species such as H+, NO2+, electron-deficient species such as BF3, AlCl3 | Example: All negatively charged species such as OH–, CN–, electron-rich species H2O, NH3 |
