Evaluate the stereochemical and mechanistic rules regarding the addition of halogens () and hydrogen halides () to carbon-carbon double bonds. Which of the following statements are chemically accurate

Question

Evaluate the stereochemical and mechanistic rules regarding the addition of halogens ($X_2$) and hydrogen halides ($HX$) to carbon-carbon double bonds. Which of the following statements are chemically accurate?

Prashant Kotian · Accepted Answer

Correct answer: A,C. A) True. The bridged halonium ion physically blocks front-side attack, forcing the halide nucleophile to attack from the back (anti-addition). B) False. Anti-addition of a symmetric reagent to a trans-alkene yields a meso compound (optically inactive due to internal symmetry), not a racemic mixture. (Cis-alkenes yield racemic mixtures). C) True. The Kharasch (peroxide) effect works only for because both propagation steps (radical addition to alkene and hydrogen abstraction from ) are exothermic. For and , one of the steps is highly endothermic, preventing the chain reaction. D) False. In the dark (absence of peroxides), follows electrophilic addition (Markovnikov's rule), yielding the more substituted product.

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