Question

Consider the sets I, II and III. Identify the set(s) which is (are) correctly matched.
[I.] Staggered ethane>eclipsed ethane \dotfill torsional strain
[II.] 2,2-Dimethylbutane>2-methylpentane \dotfill boiling point
[III.] cis-But-2-ene>trans-But-2-ene \dotfill dipole moment

• A. I, II only
• B. II, III only
• C. III only
• D. I, II, III

Hint:

Dipole moment is higher in cis-isomers due to net vector addition of bond dipoles. More branching in hydrocarbons lowers boiling point due to decreased surface area.

Answer 1

The Correct Option is C

Let's evaluate each set: - Set I: Incorrect — Staggered ethane is more stable than eclipsed ethane due to **less torsional strain**, but this is not a matching statement, because it implies staggered has *more* torsional strain, which is incorrect. - Set II: Incorrect — 2,2-Dimethylbutane has more branching than 2-methylpentane, hence has a \textit{lower} boiling point, not higher. So, this match is incorrect. - Set III: Correct — cis-But-2-ene has a net dipole moment due to polar bonds pointing in the same direction, whereas trans is symmetrical and has zero dipole moment. So this match is correct. Only Set III is correctly matched.