# How do E and Z isomers arise in molecules?

Dec 13, 2016

Geometric isomerism presumes the SAME structural isomerism, i.e. the same connectivity, however different geometry for the same structure. Organic chemistry provides rich examples of structural and geometric isomerism, and $E , Z$ or $\text{cis/trans}$ isomerism provides many instances.
Consider $\text{2-butylene}$, ${H}_{3} C - C H = C H - C {H}_{3}$; this is a simple organic structure that can nevertheless generate 2 geometric isomers as shown.
For both isomers, connectivity IS THE SAME. $C 1$ connects to $C 2$ to $C 3$ to $C 4$. Nevertheless, because of the different geometry, the isomeric butenes have different structures, and chemical properties.