What is an Electrophile

An electrophile is a reagent consisting of an atom, ion, or molecule that accepts electron pair to form a bond. It is an electron-deficient species that can be positively charged or neutral with vacant orbitals. An electrophile reacts with a nucleophile by accepting electrons through addition and substitution reactions.

All electrophiles are Lewis acids, but not all Lewis acids are electrophiles.

Electrophile Examples

How to find and identify an electrophile

Here is a list of electrophiles.

• Cations that can accept electron pairs – H⁺, Mg²⁺, Fe³⁺, NH₄⁺, CH₃⁺,and H₃O⁺
• Molecules with an incomplete octet of electrons – BF₃ and AlCl₃
• Molecules where the central atom can have more than 8 electrons in its valence shell – SiCl₄ and SiF₄
• Molecules that can have multiple bonds between two atoms of different electronegativity – CO₂ and SO₂

Strength of an Electrophile

The strength of electrophile is given by its electrophilicity, which is the ability to attract electrons. Therefore, a positively charged species that requires electrons to obtain stability is a good and strong electrophile. Likewise, a neutral molecule that can create an empty orbital by parting with an excellent leaving group is a good electrophile. For example, a carbonyl (C=O) can add a positive charge to the carbon through resonance. Likewise, a polar compound like alkyl halide can create a proton (H⁺) since halide is an excellent leaving group.

Electrophilic Reactions

Electrophiles participate in chemical reactions with other compounds. The mechanism of these reactions is such that, first, the electrophile is generated. Then, it attacks a site rich in electrons (e.g., double bond, carbanion). These reactions are known as electrophilic addition and electrophilic substitution reactions.

Electrophilic Addition

An electrophilic species combines with another compound to form a product without losing any atoms present in the reactants.

Examples

• Water adds to ethene to form ethanol

CH₂CH₂ (ethene) + H₂O (water) → CH₂OHCH₃ (ethanol)

• Bromine adds to ethene to form dibromoethane

CH₂CH₂ (ethene) + Br₂ (bromine) →CH₂BrCH₂Br (dibromoethane)

Electrophilic Substitution

A chemical reaction in which a functional group from a compound is substituted with an electrophilic species.

Examples

• Electrophilic aromatic substitution: Bromination of benzene results in bromobenzene

C₆H₆ (benzene) + Br₂ (bromine) → C₆H₅Br (bromobenzene) + HBr (hydrogen bromide)

• Electrophilic aliphatic substitution: Chlorination of acetone results in chloroacetone

CH₃COCH₃ (acetone) + Cl₂ (chlorine) → CH₃COCH₂Cl (chloroacetone) + HCl (hydrogen chloride)

Nucleophile vs. Electrophile

A nucleophile is a species that is rich in electrons and can donate them to an electrophile. Like an electrophile, a nucleophile can undergo addition and substitution reactions. One can tell if a reaction is electrophilic or nucleophilic by looking at the regents in a chemical reaction. One way to look at the reaction mechanism is to see if the electrons move from the group being added or to the group.

Differences Between a Nucleophile and an Electrophile

	Nucleophile	Electrophile
Literal meaning	To love electron	To love nucleus
Role	Electron-rich. Donates electrons	Electron-deficient. Accepts electrons
Electron pair	Possesses a loosely-held electron pair	Possesses an empty orbital to accept electron pair
Charge	Neutral or negative	Neutral or positive
Representation	Nu, or Nu–	E or E+
Alternative name	Lewis base	Lewis acid
Chemical reactions	Nucleophilic addition and nucleophilic substitution	Electrophilic addition and electrophilic substitution
Examples	Chloride ion (Cl–), ammonia (NH3), and carbanion (R’HC–R)	Hydronium ion (H+), boron trifluoride (BF3), and carbocation (R’HC+R)

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