Chemistry Learner

It's all about Chemistry

Home / Organic chemistry / Electrophile

Electrophile

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

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 valance shell – SiCl4 and SiF4
  • Molecules that can have multiple bonds between two atoms of different electronegativity – CO2 and SO2
Electrophile Examples

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

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

NucleophileElectrophile
Literal meaningTo love electronTo love nucleus
RoleElectron-rich. Donates electronsElectron-deficient. Accepts electrons
Electron pairPossesses a loosely-held electron pairPossesses an empty orbital to accept electron pair
ChargeNeutral or negativeNeutral or positive
RepresentationNu, or NuE or E+
Alternative nameLewis baseLewis acid
Chemical reactionsNucleophilic addition and nucleophilic substitutionElectrophilic addition and electrophilic substitution
ExamplesChloride ion (Cl), ammonia (NH3), and carbanion (R’HCR)Hydronium ion (H+), boron trifluoride (BF3), and carbocation (R’HC+R)
Nucleophile vs Electrophile

FAQs

Q.1. What is electrophile in sulphonation of benzene?

Ans. During sulphonation of benzene, sulfur trioxide and fuming sulfuric acid are added to the benzene. Hence, the electrophile is the sulfur trioxide (SO3).

Q.2. What is the electrophile in the nitration of benzene?

Ans. During the nitration of benzene, nitric acid and sulfuric acid are added to the benzene. Hence, the electrophile is a nitronium ion (NO2+).

Q.3. Why does benzene undergo electrophilic substitution reaction easily?

Ans. Benzene has six pi-electrons that are delocalized around the ring. Thus, it behaves like a rich source of electrons and easily attacked by reagents deficient in electrons, like nucleophiles.

References

  1. Chem.libretexts.org
  2. Chem.ucla.edu
  3. Aceorganicchem.com
  4. Chemguide.co.uk
  5. Chem.libretexts.org

Leave a Reply

Your email address will not be published. Required fields are marked *

Trending Topics