Determining when molecules are constitutional isomers

So now let’s go on to this next one. This next one what I have is I’m trying to
figure out the relationship. I see that this one has 5 carbons, this one
has 5 carbons and then I notice that both of these have the same IHD. This one has an IHD of 1 and this one also
has an IHD of 1. What does that mean? What that means is that these both have the
same molecular formula. They both have the same amount of carbons
and the same amount of hydrogens, so I would put a check mark that the molecular formula
is shared. Cool with that? Now let’s look at the connectivity. Are these connected in exactly the same way? Are all the atoms connected in exactly the
same way? The answer is no, because in one of these
I have a 5-membered ring and the other one I have a 4-membered ring. What that means is that these have different
shapes, not just shapes. These have different connectivities. For example, this one right here has a tertiary
carbon. This one over on the 5-membered ring only
has secondary carbons. So could these possibly be connected exactly
the same? No, they’re connected differently, so this
is what we would call a constitutional isomer. Just looking back, remember that a constitutional
isomer would be something that has the same molecular formula, but different connectivity
and obviously, a different shape if it’s not even connected the same.

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