I was recently studying organic chemistry related to Isomerism. I have doubt based on an example that is,
- Why Cumulenes show GI?
- Why 1-chloro cyclohexene don't show GI?
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The basic idea of geometrical isomerism is the difference between the spatial arrangement of atoms/groups between two compounds which have same molecular formulae and connectivity. One way of judging GI is analysing the difference between the distances of groups.
Cumulenes having an odd number of double bonds are capable of showing GI (granted that the two atoms/groups attached to the end carbons aren't same), however cumulenes with an even number of double bonds cannot show GI since the groups connected at the terminal carbons aren't in the same plane and are equally distant.
Don't treat double bond in a ring like a double bond in a chain. In case of a ring, for trans isomer the ring (sort of) wraps around the double bond. This is not possible in small rings due to strain and tendency to remain planar. GI around a double bond in a ring is seen from cyclooctene onwards. And it doesn't depend on the groups attached.