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JEE Main2026Jan 23, Shift 1Chemistry
Q.

But-2-yne and hydrogen (one mole each) are separately treated with (i) Pd/C and (ii) Na/liq. NH to give the products X and Y respectively.

Identify the incorrect statements.

A. X and Y are stereoisomers.

B. Dipole moment of X is zero

C. Boiling point of X is higher than Y.

D. X and Y react with O/Zn + HO to give different products.

Choose the correct answer from the options given below :

  1. A

    B and C only

  2. B

    B and D only

  3. C

    A and B only

  4. D

    A and C only

Solution

Identify X and Y. Pd/C gives syn-addition: X = cis-but-2-ene. Na/liq. NH (dissolving-metal) gives anti-addition: Y = trans-but-2-ene.

(A) True — cis and trans are stereoisomers (geometric isomers).

(B) False — cis-but-2-ene has a small but non-zero dipole moment because the two CH groups are on the same side; their bond dipoles do not cancel.

(C) True — cis isomers generally have higher boiling points (larger dipole, better packing in liquid).

(D) False — both X and Y give the same ozonolysis product (acetaldehyde, two equivalents). Geometry around C=C doesn't change which atoms end up in the cleavage fragments.

Incorrect statements are B and D only.

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