Question

How do geometric isomers differ from structural isomers?

Answer 1

Structural isomers differ in connectivity. Geometric isomers have the same connectivity, but differ in their geometry.

Explanation:

This is an old example, but still it is worthwhile in that illustrates the difference.

Consider `"but-2-ene"`. Now `"but-2-ene"` has cis and trans isomers, and I assume you can identify them. In each isomer, `C1` connects to `C2`, connects to `C3`, connects to `C4`. And thus the cis and trans isomers are structurally equivalent, because they have precisely the same connectivity. Nevertheless because `C1` can be on the opposite (or the same side) as `C4`, this simple organic molecule can generate a pair of geometric isomers in their `"cis"` and `"trans"` varieties.

The introduction of a pair of chiral centres offers further opportunities for geometric isomerism.