I understand that chain isomerism is when two molecules differ only by the classification of the carbonic chain, for example one being branched and the other straight, or one being open and the other closed. But what happens when both molecules have the same classification?
For example, 2,3-Dimethylhexane:
Both are open, branched, saturated and homogeny chains, so I don't think they have chain isomerism. Of course one have a hexane chain and the other a heptane, but that doesn't change the chain classification. I also don't see why it should be thought as a position isomerism, since the second branch wasn't exactly "moved", but incorporated in the chain.
Also, if I may, what would be the case of two unsaturated chains like Propyne and Propadiene? They're both open and unsaturated chains, so I don't know if they should be classified as a chain isomerism or a position one.