But-2-yne is reacted separately with one mole of Hydrogen as shown below: Identify the incorrect statements from the…
Hydrocarbons · Class 11 · JEE Main Previous Year Question
But-2-yne is reacted separately with one mole of Hydrogen as shown below:
Identify the incorrect statements from the options given below:
(A) A is more soluble than B.
(B) The boiling point and melting point of A are higher and lower than B respectively.
(C) A is more polar than B because dipole moment of A is zero.
(D) adds easily to B than A.
- a
(B) and (C) only
- b
(B), (C) and (D) only
- c✓
(A), (C) and (D) only
- d
(A) and (B) only
(A), (C) and (D) only
Step 1: Identify A and B
- Pd/C + H2 (Lindlar conditions): syn addition gives cis-but-2-ene = A
- Na/liq NH3 (dissolving metal): anti addition gives trans-but-2-ene = B
Step 2: Evaluate Statements
(A) A more soluble than B: Both are nonpolar hydrocarbons with similar solubility. NOT more soluble. (A) INCORRECT.
(B) BP of A higher, MP of A lower than B: cis-but-2-ene: BP = 3.7 C, MP = -138.9 C trans-but-2-ene: BP = 0.9 C, MP = -105.5 C A has higher BP than B (true) and lower MP than B (true). (B) CORRECT.
(C) A more polar, dipole moment of A is zero: cis (A) has non-zero dipole moment; trans (B) has zero dipole moment. So A IS more polar -- but the reason given (dipole of A = zero) is WRONG. (C) INCORRECT.
(D) Br2 adds easily to B than A: Both alkenes react similarly with Br2; no significant difference. (D) INCORRECT.
Incorrect: A, C, D = option (c).
Key Points:
- cis-but-2-ene (A): non-zero dipole moment; trans (B): zero dipole moment
- cis isomers: higher BP; trans isomers: higher MP
- Both isomers have similar reactivity toward Br2
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