Question

How do E and Z isomers arise in molecules?

Answer 1

Structural isomerism derives from different connectivity for a given formula.

Explanation:

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 `"cis/trans"` isomerism provides many instances.

Consider `"2-butylene"`, `H_3C-CH=CH-CH_3`; this is a simple organic structure that can nevertheless generate 2 geometric isomers as shown.

See here

For both isomers, connectivity IS THE SAME. `C1` connects to `C2` to `C3` to `C4`. Nevertheless, because of the different geometry, the isomeric butenes have different structures, and chemical properties.