key term - Electrophile

Definition

An electrophile is a species that is attracted to electron-rich regions and seeks to form new bonds by accepting electron density. Electrophiles play a crucial role in many organic reactions, including polar reactions, electrophilic aromatic substitution, and nucleophilic acyl substitution, among others.

5 Must Know Facts For Your Next Test

1. Electrophiles are attracted to regions of high electron density, such as the π-bonds of alkenes or the aromatic rings of benzene derivatives.
2. Electrophilic addition reactions, such as the halogenation of alkenes, involve the attack of an electrophile on a carbon-carbon double bond.
3. Electrophilic aromatic substitution reactions, like the bromination of benzene, occur when an electrophile replaces a hydrogen atom on an aromatic ring.
4. Nucleophilic acyl substitution reactions, including the formation of esters from carboxylic acids and alcohols, involve the attack of a nucleophile on an electrophilic carbonyl carbon.
5. Enolate ions, generated from the deprotonation of carbonyl compounds, can act as nucleophiles in reactions with electrophiles, such as alkyl halides.

Review Questions

• Explain how electrophiles are involved in the halogenation of alkenes, and describe the mechanism using curved arrow notation.
  • In the halogenation of alkenes, an electrophilic halogen molecule (e.g., $\text{Br}_2$) is attracted to the π-bond of the alkene. Using curved arrow notation, the electrophile attacks the alkene, forming a cyclic bromonium ion intermediate. A nucleophile, such as a halide ion, then attacks the cyclic intermediate, displacing the halogen and forming the haloalkane product.
• Discuss the role of electrophiles in electrophilic aromatic substitution reactions, using the Friedel-Crafts alkylation as an example.
  • In electrophilic aromatic substitution reactions, an electrophile attacks the electron-rich aromatic ring, replacing a hydrogen atom. For example, in the Friedel-Crafts alkylation, an alkyl halide acts as an electrophile and is attracted to the π-electrons of the benzene ring. With the assistance of a Lewis acid catalyst, such as $\text{AlCl}_3$, the electrophile binds to the ring, forming a carbocation intermediate. A hydride is then eliminated, resulting in the alkylated aromatic product.
• Analyze the role of electrophiles in nucleophilic acyl substitution reactions, specifically in the formation of esters from carboxylic acids and alcohols.
  • Nucleophilic acyl substitution reactions involve the attack of a nucleophile on an electrophilic carbonyl carbon. In the formation of esters from carboxylic acids and alcohols, the carbonyl carbon of the carboxylic acid acts as an electrophile, attracting the nucleophilic oxygen of the alcohol. This results in the displacement of the hydroxyl group and the formation of the ester product. The use of an acid catalyst, such as sulfuric acid, can further enhance the electrophilicity of the carbonyl carbon, facilitating the nucleophilic attack and ester formation.

Related terms

Nucleophile:

A nucleophile is a species that is attracted to electron-poor regions and seeks to form new bonds by donating electron density.

Polar Reaction:

A polar reaction is a reaction in which the formation or breaking of a bond is accompanied by the development of a partial positive or negative charge on the atoms involved.

Curved Arrow Notation:

Curved arrow notation is a graphical representation used to depict the movement of electron pairs during the course of a chemical reaction.