Carbocation rearrangements in addition

26 questions on Carbocation rearrangements in addition from the Organic Reaction Mechanisms II: Electrophilic and Radical Reactions chapter: 5 NEET level, 11 JEE Main, 10 JEE Advanced. Each one opens with its answer and solution.

• 3-Methylbut-1-ene reacts with HBr in the absence of peroxide. The major product is NEET level
• Which carbocation is the most stable? NEET level
• Oxymercuration-demercuration of alkenes is generally free from rearrangement because NEET level
• A 1,2-hydride shift in the carbocation (CH3)2CH-CH+-CH3 gives NEET level
• 3,3-Dimethylbut-1-ene reacts with HCl. The major product is NEET level
• 3-Methylbut-1-ene is treated with dilute H2SO4 in water. The major product is JEE Main level
• 3-Methylbut-1-ene reacts with HBr in the presence of peroxide. The major product is JEE Main level
• Vinylcyclohexane (CH2=CH-C6H11, a cyclohexane ring carrying a vinyl group) reacts with HBr without peroxide. The major product is JEE Main level
• 3,3-Dimethylbut-1-ene is hydrated with dilute H2SO4. The major product is JEE Main level
• 3,3-Dimethylbut-1-ene is treated with Hg(OAc)2, H2O and then NaBH4. The major product is JEE Main level
• Assertion: Oxymercuration-demercuration of 3,3-dimethylbut-1-ene gives 3,3-dimethylbutan-2-ol without any methyl shift. Reason: The intermediate is a bridged me... JEE Main level
• Which of the following alkenes gives NO rearranged product when treated with HCl (no peroxide)? JEE Main level
• 3-Methylbut-1-ene is treated with BH3.THF and then H2O2/NaOH. The major product is JEE Main level
• 3,3-Dimethylbut-1-ene is treated with HBr in the presence of peroxide. The major product is JEE Main level
• 3,3-Dimethylbut-1-ene reacts with HCl and the major product is formed through a 1,2-methyl shift. Count the number of CH3 groups (carbons bonded to three hydrog... JEE Main level
• Which of the following alkenes give a rearranged alkyl bromide as the major product with HBr in the absence of peroxide? JEE Main level
• An alkene X (C6H12) gives 3,3-dimethylbutan-1-ol on treatment with BH3.THF and then H2O2/NaOH. The same alkene X with dilute H2SO4 gives mainly 2,3-dimethylbuta... JEE Advanced level
• For which alkene do Hg(OAc)2/H2O then NaBH4 and dilute H2SO4 give the same alcohol, while BH3.THF then H2O2/NaOH gives a different alcohol? JEE Advanced level
• 3,3-Dimethylbut-1-ene is treated with (i) HI in the presence of peroxide and (ii) HBr in the presence of peroxide. The major products are JEE Advanced level
• Assume the secondary cation (cyclobutyl)-CH+-CH3 from protonation of vinylcyclobutane rearranges, by ring expansion and then a hydride shift, until the cation i... JEE Advanced level
• 3-Methylbut-1-ene is converted to an alcohol in three separate ways: (1) Hg(OAc)2, H2O then NaBH4; (2) dilute H2SO4; (3) BH3.THF then H2O2/NaOH. Each alcohol is... JEE Advanced level
• 1-Methylcyclohexene reacts with (i) HBr in the dark with no peroxide and (ii) HBr with peroxide. Which pair gives the constitution of the major products? JEE Advanced level
• Which reactions involve a skeletal rearrangement (hydride or methyl shift) as the main pathway? JEE Advanced level
• Which carbocations can rearrange by a 1,2-shift to a more stable carbocation? JEE Advanced level
• 3,3-Dimethylbut-1-ene reacts with HBr (no peroxide). Which statements are correct? JEE Advanced level
• 3-Methylbut-1-ene reacts with HBr with and without peroxide. Which statements are correct? JEE Advanced level