Question

First, you name both the compounds. Yes, both of them have the same name. Yet, are they really the same structure, or they are somehow different? Careful inspection should convince you that they are indeed different. Now, how their physical and chemical properties differ? Generally,
i) Cis-isomer has more dipole moment than trans-isomer.
ii) Cis is less stable than trans.
iii) The boiling points of cis isomers are more than those of trans isomers (remember boiling points are directly related to polarity which is determined by dipole moment).
iv) Chemical reactivities of cis and trans also differ from each other.

Arrange the following compounds in the increasing order of their boiling points.

(A) $C{H}_3-CH=CH-C{H}_3\left(cis\right)$
(B) $C{H}_3-CH=CH-C{H}_3\left(trans\right)$
(C) $C{H}_3-CH=CHCl\left(cis\right)$
(D) $C{H}_3-CH=CHCl\left(trans\right)$

• A. B < A < C < D
• B. D < B < A < C
• C. B < A < D < C
• D. C < A < B < D

Answer 1

The correct option is C B < A < D < C

= Cis form has more boiling point than trans because of more polarity and larger surface area.
= Cis form has more dipole moment than trans.
So, B. P. of A > B. P. of B
B. P. of C > B. P. of D
B. P. of C > B. P. of A
C has more molecular mass compared to, A and hence more surface area for boiling.