Determine Products of Electrophilic Addition Reactions

 

 

← Back to Alkenes

 

  1. The electrophile (species with + or δ+) is added to the C=C first
  2. The electrophile is added to the C with more H (Markonikov’s Rule)
  3. Presence of competing nucleophiles can lead to a mixture of products

 

Question. When alkenes are reacted with mixed halogens e.g. I―Cl, which atom is the electrophile; which atom is added to the C=C first?

 

Answer. Compare the electronegativity of the halogens. The less electronegative element is the electrophile; it is added first and to the C with more H.

 

Example (for 1+2):

  • I is less electronegative compared to Cl
  • I is added first and to the C with more H

 

Example (for 3):

  • Reagent used is Br2 (aq) [c.f. Br2 (in CCl4)]
  • There are two possible nucleophiles in the 2nd step: Br– and H2O
  • A mixture of products would be obtained