One equivalent of H2 is added to 4-phenylbut-3-en-2-one, C6H5-CH=CH-CO-CH3, over Pd-C at 1 atm and room temperature. The major product is

JEE Main levelSingle correct optionDifficulty 2 of 3ro116

One equivalent of $H X_{2}$ is added to 4-phenylbut-3-en-2-one, $C X_{6} H X_{5} - CH = CH - CO - CH X_{3}$ , over Pd-C at 1 atm and room temperature. The major product is

Under mild Pd-C hydrogenation the conjugated

C = C

is reduced much faster than the ketone or the benzene ring. One equivalent of

H X_{2}

therefore saturates only the double bond to give

C X_{6} H X_{5} - CH X_{2} CH X_{2} - CO - CH X_{3}

, 4-phenylbutan-2-one.