Given below are two statements : In the light of the above statements, choose the most appropriate answer from the options given below :
- Both Statement I and Statement II are correct
- Statement I is incorrect but Statement II is correct
- Both Statement I and Statement II are incorrect
- Statement I is correct but Statement II is incorrect
Answer
(4) Statement I is correct but Statement II is incorrect
Solution
Statement I: In cis-1,2-dihaloethenes the two C–X bond moments add up. Cl is more electronegative than Br, so the C–Cl bond moment is larger.
cis-1,2-dichloroethene (μ ≈ 1.90 D) is more polar than cis-1,2-dibromoethene (μ ≈ 1.35 D). Correct.
Statement II: As per NCERT, cis isomers have higher boiling points than trans isomers (stronger dipole–dipole forces), so the boiling point of trans-1,2-dibromoethene is lower than that of the cis isomer — this part is true. But in the trans isomer the two C–Br bond moments cancel (μ = 0), so it is less polar, not more polar, than the cis isomer. Incorrect.
Statement I is correct but Statement II is incorrect.
Answer: (4)