Addition of HBr to propene: Markovnikov rule and peroxide effectप्रोपीन पर HBr का योग: मारकोनीकॉफ़ नियम और परॉक्साइड प्रभाव

NCERT Sec 9.3.5 · interactive diagram

Parts and their functions

• Unsymmetrical alkene + HBr (असममित ऐल्कीन + HBr) — Propene is unsymmetrical, so HBr can add in two ways; the product depends on the intermediate formed.
• Ionic path (electrophilic addition) (आयनिक मार्ग (इलेक्ट्रॉनस्नेही योगज)) — H⁺ attacks the π bond. It can give a 2° carbocation (CH₃C⁺HCH₃) or a 1° one (CH₃CH₂C⁺H₂); the 2° ion is more stable (hyperconjugation, +I), so it forms faster.
• Markovnikov product (मारकोनीकॉफ़ उत्पाद) — Br⁻ attacks the 2° carbocation → 2-bromopropane. Rule: the negative part of the addendum goes to the carbon with fewer H atoms.
• Free-radical path (Kharash effect) (मुक्त-मूलक मार्ग (खराश प्रभाव)) — Benzoyl peroxide gives C₆H₅• which takes H from HBr to give Br•. Br• adds to the terminal CH₂ to form the more stable 2° radical CH₃C•HCH₂Br.
• Anti-Markovnikov product (प्रति-मारकोनीकॉफ़ उत्पाद) — The radical takes H from HBr → 1-bromopropane, and Br• is regenerated (chain). Works only with HBr — not HCl or HI.
• One idea behind both (दोनों के पीछे एक विचार) — In both paths the more stable intermediate (2° > 1°) forms; what differs is which atom adds first — H⁺ (ionic) or Br• (radical).

Original diagram drawn by Simple Learning Hub, based on NCERT Sec 9.3.5. Report a mistake