3-phenylpropene on reaction with HBr gives (as a major product) (a) C6 H5 CH2 CH(Br) CH3 (b) C6

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3-phenylpropene on reaction with HBr gives (as a major...

3-phenylpropene on reaction with HBr gives (as a major product) (a) $\mathrm{C}_{6} \mathrm{H}_{5} \mathrm{CH}_{2} \mathrm{CH}(\mathrm{Br}) \mathrm{CH}_{3}$ (b) $\mathrm{C}_{6} \mathrm{H}_{5} \mathrm{CH}(\mathrm{Br}) \mathrm{CH}_{2} \mathrm{CH}_{3}$ (c) $\mathrm{C}_{6} \mathrm{H}_{3} \mathrm{CH}_{2} \mathrm{CH}_{2} \mathrm{CH}_{2} \mathrm{Br}$ (d) $\mathrm{C}_{6} \mathrm{H}_{5} \mathrm{CH}(\mathrm{Br}) \mathrm{CH}=\mathrm{CH}_{2}$

3-phenylpropene on reaction with HBr gives (as a major product)
(a) $\mathrm{C}_{6} \mathrm{H}_{5} \mathrm{CH}_{2} \mathrm{CH}(\mathrm{Br}) \mathrm{CH}_{3}$
(b) $\mathrm{C}_{6} \mathrm{H}_{5} \mathrm{CH}(\mathrm{Br}) \mathrm{CH}_{2} \mathrm{CH}_{3}$
(c) $\mathrm{C}_{6} \mathrm{H}_{3} \mathrm{CH}_{2} \mathrm{CH}_{2} \mathrm{CH}_{2} \mathrm{Br}$
(d) $\mathrm{C}_{6} \mathrm{H}_{5} \mathrm{CH}(\mathrm{Br}) \mathrm{CH}=\mathrm{CH}_{2}$

Key Concepts

Electrophilic Addition Reaction

In organic chemistry, electrophilic addition is a fundamental reaction mechanism in which an electrophile adds to a multiple bond, such as an alkene or alkyne, to form a saturated compound. The process typically involves the initial attack of the ?-electrons of the double bond on an electrophilic species, generating a carbocation intermediate that is subsequently attacked by a nucleophile. This type of reaction is central to a wide range of synthetic transformations.

Carbocation Intermediate Stability

The formation and stability of carbocation intermediates play a crucial role in determining the outcome of electrophilic addition reactions. More stable carbocations, such as those that are tertiary, benzylic, or allylic, form more readily and guide the reaction pathway. The stability is often governed by hyperconjugation and resonance effects, which lower the energy of the intermediate and favor its formation.

Markovnikov's Rule

Markovnikov's rule is an empirical guideline used to predict the regiochemistry of the addition of protic acids to alkenes. It states that in the addition of HX to an unsymmetrical alkene, the hydrogen atom bonds to the carbon with more hydrogen substituents, while the halide bonds to the carbon with fewer hydrogen substituents. This rule arises from the preferential formation of the more stable carbocation intermediate during the reaction.

Resonance Stabilization

Resonance stabilization refers to the delocalization of electrons in a molecule, which can significantly enhance the stability of certain intermediates such as carbocations. In molecules where a positive charge can be delocalized over an aromatic ring or through adjacent ?-bonds, the resulting resonance-stabilized carbocations are lower in energy and more favored during the reaction process. This stabilization is essential for understanding regioselectivity in electrophilic addition reactions involving unsymmetrical alkenes.

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