Lindlar-catalyzed hydrogenation of phenylacetylene produces which product?

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Multiple Choice

Lindlar-catalyzed hydrogenation of phenylacetylene produces which product?

Lindlar-catalyzed hydrogenation reduces alkynes to alkenes and stops there because the catalyst is poisoned to prevent further hydrogenation to alkanes. The hydrogen adds syn, giving a cis-alkene. For a terminal alkyne like phenylacetylene (Ph–C≡CH), this partial hydrogenation yields styrene (Ph–CH=CH2). In this case there isn’t a meaningful E/Z designation for the double bond, since one vinylic carbon bears two hydrogens, so the product is simply styrene. The other options would require full saturation to an alkane (ethylbenzene) or oxidation to benzaldehyde, which do not arise under Lindlar hydrogenation.

Lindlar-catalyzed hydrogenation reduces alkynes to alkenes and stops there because the catalyst is poisoned to prevent further hydrogenation to alkanes. The hydrogen adds syn, giving a cis-alkene. For a terminal alkyne like phenylacetylene (Ph–C≡CH), this partial hydrogenation yields styrene (Ph–CH=CH2). In this case there isn’t a meaningful E/Z designation for the double bond, since one vinylic carbon bears two hydrogens, so the product is simply styrene. The other options would require full saturation to an alkane (ethylbenzene) or oxidation to benzaldehyde, which do not arise under Lindlar hydrogenation.

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