Reactions of alkenes - Free MCQ Practice Test with solutions, JEE Chemistry

Hydroboration oxidation reaction.

Alkenes do not undergo mercuration, indeed they undergo oxymercuration , a process in which an alkene is converted into an alcohol.

The reaction is hydroboration which is addition of H₂O to alkene (anti Makownikoff's's rule)

Anti-Markownikoff addition is possible only in case of HBr and not in HCl and HI. In HBr both the chain initiation and propagation steps are exothermic, while in HCl, first step is exothermic, and second step is endothermic and in HI, no step is exothermic. Hence HCl and HI do not undergo antiMarkownikoff's addition.

Oxymercuration - demercuration reaction addition of H₂O molecule is according to Markovnikoff's rule.

The addition of HI on the double bond of propene yields isopropyl iodide and not n-propyl iodide as the major product. This is because the addition proceeds through a more stable carbonium ion.

A molecule of Hbr is added to C = C double bond. Br is added to less substituted terminal carbon atom. (The anti markonikov's addition of HBr to unsymmetrical alkenes in presence of peroxides)

Option D is correct.

Alkaline potassium permanganate adds two hydroxyl groups across a double bond by syn addition, giving a vicinal diol.

When syn addition occurs on a trans (oppositely substituted) disubstituted alkene, the two new stereocentres are formed with the same absolute configuration in one product and the opposite configuration in the other; these two products are non-superimposable mirror images.

Therefore the reaction of the given trans alkene with cold, aqueous alkaline KMnO4 yields a racemic mixture of the enantiomers (R,R) and (S,S) of 2,3-butanediol, produced by syn addition.

Fomation of A is hydration by Markownikov's orientation. Fomation of B is by HEO reaction (An Markomilkov's orentation)

benzene not decolurise bromine water solution , and only 3 option has 0 degre of unsaturation