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JEE Main 2025 Jan 22 Shift 1, Chemistry Q20: Stereoisomerism

JEE Main2025Jan 22, Shift 1Chemistry
Q.

The incorrect statements regarding geometrical isomerism are :

(A) Propene shows geometrical isomerism.

(B) Trans isomer has identical atoms/groups on the opposite sides of the double bond.

(C) Cis-but-2-ene has higher dipole moment than trans-but-2-ene.

(D) 2-methylbut-2-ene shows two geometrical isomers.

(E) Trans-isomer has lower melting point than cis isomer.

Choose the CORRECT answer from the options given below :

  1. A

    (A), (D) and (E) only

  2. B

    (C), (D) and (E) only

  3. C

    (B) and (C) only

  4. D

    (A) and (E) only

Solution

(A) Propene (CHCHCH) has two identical H atoms on one of the doubly-bonded carbons, so it does not show geometrical isomerism. Incorrect statement.

(B) True in a trans isomer the two identical (or higher-priority) groups lie on opposite sides of the CC bond.

(C) True in cis-but-2-ene the two methyl dipoles add partially; in trans-but-2-ene they cancel. So .

(D) 2-Methylbut-2-ene, , has two identical methyl groups on one sp carbon, so geometrical isomerism is impossible. Incorrect statement.

(E) Generally trans isomers pack better in the crystal and have higher melting points than cis. Saying trans has a lower m.p. is incorrect.

The incorrect statements are (A), (D), and (E).

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