Question

When shown diagrams of isomers, how can you determine which is a structural and which is a geometric isomer?

Answer 1

The isomers of different connectivity are......

Explanation:

....structural isomers. The isomers with the same connectivity, but different geometry, are geometric isomers.

The word `"connectivity"` is key. Consider `"2-butylene"`, which structure can generate both cis and trans geometric isomers. For both geometries the connectivity is the same: `"C1 connects to C2, which connects to...C4"`. Nevertheless, the cis and trans isomers are manifestly different with respect to geometry, and are thus geometric isomers, or even diastereomers. (Note, here I use the definition that diastereomers are geometric isomers that are not mirror images.)