Electrophilic addition

In organic chemistry, an electrophilic addition reaction is an addition reaction where in chemical compound a pi bond is removed by the creation of two new covalent bonds. In electrophilic additions 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 a electron-rich unsaturated system (-C=C-) (step 1). 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.

Typical reactions are:

• the dihalo addition reaction
• Hydrohalogenation
• the Hydration reaction
• Hydrogenation

In all asymmetric addition reactions to carbon regioselectivity is important and often determined by Markovnikov's rule.