Electrophilic addition: an overview

• Electrophilic addition is a fundamental chemical reaction where an electrophile and a nucleophile, typically an alkene or alkyne, combine to form a single bond.
• This process involves the conversion of a π bond into new σ bonds, playing a crucial role in the transformation of alkenes and alkynes into more complex organic compounds.

Key Concepts of Electrophilic Addition

1. Electrophiles and Nucleophiles:

   • Electrophiles are electron-deficient species that seek electrons.
   • Nucleophiles are electron-rich species ready to donate electrons.
   • Alkenes and alkynes act as nucleophiles due to their electron-rich π bonds.

2. Mechanism of Electrophilic addition:

   • The reaction occurs in two main steps:
     • Step 1: Electrophilic Attack:
       The electrophile attacks the electron-rich π bond, forming a carbocation intermediate.
     • Step 2: Nucleophilic Attack:
       The nucleophile then attacks the carbocation, forming a new σ bond.

Example: Addition of HBr to Ethene

1. Step 1 – Electrophilic Attack:

   • HBr’s proton (H⁺) acts as the electrophile, attacking the ethene’s π bond, forming a carbocation and a bromide ion (Br⁻).
   • H₂C=CH₂ + HBr → H₂C-CH₂⁺ + Br⁻

2. Step 2 – Nucleophilic Attack:

   • The bromide ion (Br⁻) then attacks the carbocation, forming bromoethane.
   • H₂C-CH₂⁺ + Br⁻ → H₂C-CH₂Br

Significance of Electrophilic addition

• Electrophilic addition is vital in organic synthesis, allowing for the introduction of functional groups into alkenes and alkynes.
• This versatility makes it indispensable in creating a myriad of organic compounds, including polymers, pharmaceuticals, and agrochemicals.
• By employing different electrophiles, such as hydrogen halides (HX), halogens (X₂), and water (H₂O), chemists can synthesize a diverse range of functionalized molecules through this reaction mechanism.

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