Question

Why are there cis and trans isomers?

Answer 1

Because this a geometric consequence of structural chemistry.

Explanation:

For olefins, say `"2-butene"` and rings, say `1,2-"dimethylcyclohexane"` the geometry of the structure dictates that the methyl groups can be on the same side of the double bond or the ring (the cis isomer), or on the opposite sides of the double bond of the ring, the trans isomer). These are geometric isomers because connectivity is the same for both examples, and yet geometry is markedly different.