Consider the electrophilic addition of hydrogen bromide () to 1-phenylpropene () in a dark environment without any peroxides. After the reaction is complete, what is the absolute total number of -elec

Question

Consider the electrophilic addition of hydrogen bromide ($HBr$) to 1-phenylpropene ($C_6H_5-CH=CH-CH_3$) in a dark environment without any peroxides. After the reaction is complete, what is the absolute total number of $\pi$ -electrons remaining in the structure of the major organic product formed?

Prashant Kotian · Accepted Answer

Correct answer: 6. The reaction follows Markovnikov's rule via electrophilic addition. The adds to the alkene to form the most stable carbocation intermediate. Adding to C2 yields a benzylic carbocation (), which is highly stabilized by resonance with the adjacent phenyl ring. Adding to C1 yields a carbocation. Thus, the benzylic cation dominates. The then attacks to form 1-bromo-1-phenylpropane. While the alkene pi-bond has been saturated and destroyed, the aromatic phenyl ring remains completely intact. A standard benzene ring contains exactly 6 delocalized -electrons.

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