Why do E and Z isomers occur?

1 Answer
anor277 · MeneerNask
Oct 13, 2016

Because an olefin does not allow free rotation around the double bond.

Explanation:

For even a simple olefin such as #"2-butylene"#, geometric isomerism can occur because of the #C=C# bond. The methyl groups can be on the same side of the #C=C# bond to give the #"cis"# or #"Z"# isomer, or on opposite sides of the #C=C# bond to give the #"trans"# or #"E"# isomer.

Both isomers have the same #C-C# connectivity: #C1# connects to #C2#......to......#C4#, yet they are manifestly different geometrically. They are thus diastereomeric, and should give rise to different chemical and physical properties, and indeed they do.
enter image source here
enter image source here

Related questions
See all questions in E and Z
Impact of this question
2218 views around the world
You can reuse this answer
Creative Commons License