Give the major product that forms when 1 -ethylcyclohexene...

Give the major product that forms when 1 -ethylcyclohexene 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 1 -ethylcyclohexene 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

Acid-Catalyzed Hydration

Acid-catalyzed hydration is the addition of water to an alkene in the presence of a strong acid like H2SO4. The acid protonates the alkene to form a carbocation intermediate, which is then attacked by water. Subsequent deprotonation yields an alcohol. The reaction is governed by Markovnikov's rule, meaning that the hydroxyl group generally attaches to the more substituted carbon, generating a more stable intermediate.

Halogen Addition Reaction

The halogen addition reaction to alkenes involves the addition of a diatomic halogen, like Br2, to the double bond. This reaction proceeds through a cyclic halonium ion intermediate which is subsequently opened by a halide ion, leading to the formation of a vicinal dihalide. The reaction is stereospecific and typically results in anti addition, meaning that the two new bonds form on opposite faces of the alkene.

Electrophilic Addition to Alkenes

This concept involves the addition of an electrophile, such as a hydrogen halide, to the carbon–carbon double bond in alkenes. In these reactions, the alkene acts as a nucleophile and attacks the electrophile, leading to the formation of a carbocation intermediate that is then attacked by a nucleophile. Regioselectivity plays a key role here, with the addition often following Markovnikov’s rule, where the proton adds to the less substituted carbon to generate a more stable carbocation.

Catalytic Hydrogenation

Catalytic hydrogenation is the process of adding molecular hydrogen (H2) to an alkene in the presence of a metal catalyst, such as platinum, palladium, or nickel. This reaction occurs via the adsorption of both the alkene and hydrogen onto the catalyst surface, allowing the transfer of hydrogen atoms to the double bond, thereby converting the alkene into a saturated alkane. The reaction is stereospecific and typically results in syn addition.

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