Electrophilic addition

In organic chemistry, an electrophilic addition reaction is an addition reaction where, in a chemical compound, a pi bond is removed by the creation of two new covalent bonds. In Electrophilic addition reactions, common substrates have a carbon-carbon double bond or triple bond.

Y-Z + C=C → Y-C-C-Z

The driving force for this reaction is the formation of an electrophile Y⁺ that forms a covalent bond with an electron-rich unsaturated C=C bond. The positive charge on Y is transferred to the carbon-carbon bond.

Step (1) Y⁺ + C=C → Y-C-C⁺-

In step 2 of an Electrophilic addition, the positively charged intermediate combines with (Z) that is electron-rich to form the second covalent bond.

Step (2) Y-C-C⁺- + Z → Y-C-C-Z

Step 2 is also found in a SN1 reaction. The exact nature of the electrophile and the nature of the positively charged intermediate is not always clear and depends on reactants and reaction conditions.

In all asymmetric addition reactions to Carbon Regioselectivity is important and often determined by Markovnikov's rule. Organoborane compounds give anti-Markovnikov additions. Electrophilic attack to an aromatic system results in electrophilic aromatic substitution rather than an addition reaction.

Typical electrophilic additions

Typical electrophilic additions to alkenes with reagents are:
* dihalo addition reactions: X₂
* Hydrohalogenations:HX
* Hydration reactions: H₂O
* Hydrogenations H₂
* Oxymercuration reactions: mercuric acetate, water
* Hydroboration-oxidation reactions : diborane
* the Prins reaction : formaldehyde, water