Question

The boiling point (in $K$ ) of cis but- 2 -ene and dipole moment (in D) of trans but-2-ene are respectively

• A. 274,0.00
• B. 277,0.00
• C. 277,0.33
• D. 274,0.33

Answer 1

Answer: (B)

Boiling point $=3.7^{\circ }C(\approx 277K)$

$\mu =0.33D$

cis-but-2-ene has higher dipole-dipole attraction than trans isomer hence, has high boiling point.



Boiling point $=0.9={}^{\circ }C(\simeq 274k)$

$\mu =0D$

The dipole moment of trans-but-2-ene is zero, because the bond dipoles cancel each other.

However, the dipole moment of $cis$ -but- 2 -ene is $0.33D$, the vector sum of the two bond dipoles.