Question

The two images of 1, 2-dichloroethene are attached to this question. Can we call them isomers?

A.Yes
B.No
C.Maybe
D.Can’t say

Answer 1

Hint:These two molecules in the picture are not the same. The carbon-carbon double bond won't rotate and so we have to take the models to pieces in order to convert one structure into the other one. That is a simple test for isomers. If we take a model to pieces to convert it into another one, then we have got isomers.

Complete step by step answer:
The two molecules are the two isomers of 1,2-dichloroethene. The first molecule, the two chlorine atoms are locked on opposite sides of the double bond. This is known as the trans isomer. The word trans comes from the Latin word which means ‘across’.
The second molecule, the two chlorine atoms are locked on the same side of the double bond. This is known as the cis isomer. The word cis comes from the Latin word which means ‘on this side’.The first molecule is the trans isomer and the second molecule is the cis isomer.
So, yes, these two can be called as isomers.
Therefore, the correct answer is option (A).

Note: Isomers are the molecules whose molecular formula are same, but the arrangement of the atoms in space is different. That will exclude any different arrangements which are simply due to the molecule rotating as a whole, or rotating about particular bonds. 1,2-Dichloroethene is commonly called 1,2-dichloroethylene or 1,2-DCE. It is an organochlorine with the molecular formula ${C_2}{H_2}C{I_2}$ . 1,2-Dichloroethene is a highly flammable, and colourless liquid with a sharp, harsh smell.