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Constitutional Isomers

Posted: Fri Mar 10, 2017 7:58 pm
by Annie Duong 3L
Hi,
I still don't understand how to come up with constitutional isomers. For example, when they ask for the cycloalkane isomers of C8H16, how do I figure it out?

Re: Constitutional Isomers

Posted: Fri Mar 10, 2017 8:31 pm
by Christopher Reed 1H
Constitutional isomers are compounds that have the same molecular formula and different connectivity. They will all have different names.

So any cycloalkane where I can count up 8 carbons and 16 hydrogens is a constitutional isomer. One of the easiest ways to do this is to start with your basic cyclooctane and then start making the ring smaller and lengthening a substituent. So I could draw a methylcycloheptane, an ethylcyclohexane, a propylcyclopentane.

Do you see the pattern? As I "lose" a part of my ring I add to my substituent to get the correct amount of carbons and hydrogens.

Hope that helped!

Re: Constitutional Isomers

Posted: Sat Mar 11, 2017 10:35 am
by samuelkharpatin2b
When you see the term "constitutional isomer", all that simply means is that the problem is asking you to draw out a couple of different configurations of the same molecule. For example, if the compound you need to draw has a total of four carbons, you can draw that as a square, a triangle with a line sticking out from it, etc. That of course would be if they wanted you to draw it in cycloakane form. There might be times when they want you to draw it in line structures, but you would follow the same procedure, just rearrange the lines to make sure you have the same molecular formula representation every time.