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JEE Main levelSingle correct optionDifficulty 2 of 3ro238

Which reagent converts the alkyne shown into the cis (Z) alkene?

ANa, liquid $NH X_{3}$
B $H X_{2}$ , Lindlar catalyst
C $H X_{2}$ (excess), Pd/C
D $HgSO X_{4}$ , dilute $H X_{2} SO X_{4}$

Answer: B

The compound is pent-2-yne. Poisoned Pd (Lindlar) gives syn addition of

H X_{2}

and stops at (Z)-pent-2-ene. Na/

NH X_{3}

gives the E isomer, excess

H X_{2}

/Pd-C gives pentane, and mercury(II)-catalysed hydration gives a ketone.

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