Organic Chemistry Tutorials

Electrophile- What is it?

electrophile reaction

Core Concepts

In this tutorial, you will learn how to determine if a molecule can act as an electrophile. This will be done by understanding concepts about an electrophile’s structure that can affect its ability to react. Additionally, you will learn a list of electrophiles.

Topics Covered in Other Articles

Vocabulary

  • Cation- a positively charged ion
  • Covalent Bond- the sharing of electrons between two nonmetals or metal and metalloid
  • Electron- the negatively charged subatomic particle located outside the nucleus
  • Electron Sink- an electron-poor site on a molecule
  • Electrophilicity- the ability of a compound to act as an electrophile
  • Leaving group- an atom or group that can break away from a molecule
  • Resonance Structure- the different ways the electrons can move in a molecule, creating different charges and locations for potential reactions
  • Steric Hindrance- the effect that the physical size and structure of a molecule has on its reactivity

Introduction to Electrophiles

An electrophile is an electron-poor molecule that can form covalent bonds by accepting electrons from a nucleophile, an electron-rich molecule. In organic reactions, many molecules can act as an electrophile, but there are certain ways a molecule can become one. Learn more about electrophiles below!

What factors make up a good electrophile?

Charge

The potential of a molecule to act as an electrophile depends on its ability to be an electron sink and accept a negative charge. Since the molecule needs to be lacking electrons in order to accept the bond to an electron source, a positive molecule will be the best electrophile.

A neutral molecule can also be a good electrophile due to resonance. If there is a resonance structure possible, then there is most likely an electron sink at a bond site, which can accept electrons to form a bond. Additionally, in a neutral molecule, if there is a good leaving group, the removal of it can cause an orbital to empty and create a positive charge.

On the other hand, since an anion is an electron source, it cannot accept more electrons and therefore cannot be an adequate electrophile.

Bond Type

Good electrophiles typically contain weak polar or polarizable bonds. This means that electrons can favor one side of a bond over the other, creating dipoles. These bonds will contain a partial positive charge on one side, usually a carbon in a hydrocarbon molecule, and a partial negative charge on the other, usually a more electronegative compound such as oxygen; the partial positive side of the bond will be more electrophilic.

Steric Hindrance

The more crowded a potential bond site is, the less likely it is for the other molecule to be able to share its electrons to form the covalent bond. This, known as steric hindrance, increases as the number of bonds to molecules other than hydrogen adjacent to the electrophilic site increases. This can limit the type of reaction that can be performed. Therefore, the less sterically hindered a molecule is, the easier it will be for it to undergo different reactions.

To learn more about the reaction limitations, read here!

List of Electrophiles

  • Hydrogen Ion- H+
  • Hydronium Ion- H3O+
  • Acid Chlorides- CH3COCl
  • Carbon Dioxide – CO2
  • Diatomic Halogens- Br2, I2, F2
  • Alkyl Halides- CH3CH2Br

Further Reading

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