Give the major product that forms when (Z)-3-methyl2-pentene...

Give the major product that forms when (Z)-3-methyl2-pentene reacts with each of the following reagents: (a) $\mathrm{HI} ;$ (b) $\mathrm{H}_{2}$ in the presence of a platinum catalyst; (c) $\mathrm{H}_{2} \mathrm{O}$ in $\mathrm{H}_{2} \mathrm{SO}_{4} ;$ (d) $\mathrm{Br}_{2}$ in $\mathrm{CCl}_{4}$.

Give the major product that forms when (Z)-3-methyl2-pentene reacts with each of the following reagents:
(a) $\mathrm{HI} ;$ (b) $\mathrm{H}_{2}$ in the presence of a platinum catalyst; (c) $\mathrm{H}_{2} \mathrm{O}$ in $\mathrm{H}_{2} \mathrm{SO}_{4} ;$ (d) $\mathrm{Br}_{2}$ in $\mathrm{CCl}_{4}$.

Key Concepts

Electrophilic Addition Reactions

These reactions involve the attack of an electron?rich alkene on an electrophile, leading to the formation of cyclic intermediates or carbocations. The specific reagents such as hydrogen halides, water, and halogens add across the double bond, and the regiochemistry and stereochemistry of the addition are often governed by the stability of intermediates and the mechanism involved.

Markovnikov's Rule

This rule predicts that in electrophilic additions involving unsymmetrical reagents (like HX or H2O in acid), the hydrogen atom tends to add to the carbon with more hydrogen substituents, leading to the more stable carbocation intermediate. This concept is central when determining the major product in such addition reactions.

Catalytic Hydrogenation

A reaction in which dihydrogen (H2) is added across an alkene's double bond in the presence of a metal catalyst, such as platinum. This process results in the conversion of the alkene into a saturated alkane, with syn addition of hydrogen atoms to the same face of the former double bond.

Acid-Catalyzed Hydration

This is a specific type of electrophilic addition where water, in the presence of an acid like H2SO4, adds across an alkene to form an alcohol. The mechanism typically proceeds via the formation of a carbocation intermediate and follows Markovnikov's rule, where the hydroxyl group attaches to the more substituted carbon.

Halogen Addition via Bromonium Ion Formation

When alkenes react with diatomic halogens such as Br2 in an inert solvent like CCl4, the mechanism involves the formation of a cyclic bromonium ion intermediate. Nucleophilic attack by a halide ion occurs from the backside, leading to anti addition and the formation of vicinal dihalides with specific stereochemical outcomes.

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