I'm reading a high school chemistry course online, and I'm now reading about geometric isomers.
They provide this example:
And in terms of naming it, they say this:
Begin by identifying the parent chain - it is the continuous chain that contains the carbon-carbon double bond. The two groups that belong to the parent chain are on opposite sides.
Then supply this illustration:
And with that explains that it's trans-3-ethyl-3-hexene for that reason. I don't quite get their explanation though, becuase to me it seems like this could also be cis.
Why can't it be this one:
As far as I understand, that's also a valid way of expanding it, because it has the same amount of carbons in the chain and the numbers are still as low as they get. The only difference is that this one would be cis-3-ethyl-3-hexene instead of trans-3-ethyl-3-hexene.
So, why exactly is it that only one of them is right?