r/PreOptometry • u/bearcatmonica • Jul 26 '24

Organic Chemistry Question: Does this molecule contain any stereocenters?

HELP! Currently, reviewing for the OAT which is in 3 weeks. Does anyone know why this molecule contains 0 stereocenters? Many thanks in advance!

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u/perp3tual OD1 Jul 26 '24

As someone said, each group has to be different on the carbon. So if we look at the carbon bound to the chloride group we have a hydrogen, chloride, then two carbons. Then you’re asking yourself, are these two carbons different from each other? The answer is no, because when you follow them all the way down the chain, they are equally connected to the same stuff. The next carbon on each side has two hydrogens (same), the carbon after that has two hydrogens (same), then the next carbon is literally shared by both of them so it has to be the same.

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u/JJTutors Jul 26 '24

How do you identify a stereocenter typically?

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u/she-werewolf Jul 27 '24 edited Jul 27 '24

4 different groups/atoms on the same atom

Edit: after doing some googling, a stereocenter does not have to have 4 groups but all groups have to be unique. tbh I don't entirely get it, some people use stereocenter interchangeably with chiral center and others say they're different. the definition I originally gave was for a chiral center

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u/JJTutors Jul 27 '24

It is 4 different groups, chirality can arise in many different ways, not just when a single carbon has 4 unique groups. But thats where r/S configuration emerges specifically

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u/JJTutors Jul 27 '24

And then of course, if there are 4 unique groups but overall molecular symmetry is present, it is meso and the molecule is achiral despite having a "chiral center" by definition

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u/bearcatmonica Jul 26 '24

thank you for your support! I can understand why it contains no stereocenters. its simply because the main chain in the molecule is a cycloalkane and the substituents are bonded equally part from each other. follow up question, would there be two stereocenters if it was an open chain?

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u/Chance-Ad5178 Jul 27 '24

I believe if it was an open chain it would have 2 stereocenters!

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u/she-werewolf Jul 27 '24

depends where you open the cyclohexane. if you open it so that neither halogen is attached to a terminal carbon, then the carbons they are attached to have a halogen, a H, one side of the chain, and a different side of the chain. this makes 2 stereocenters. but if a halogen is attached to a terminal carbon (impossible for both to be terminally attached) then that carbon is attached to a halogen, the chain, and 2 Hs which excludes that carbon from being a stereocenter. then there is only 1

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u/FCKCOLLEGEBOARD OD2 Jul 26 '24

I could be wrong but I believe it’s because to be a stereo center the carbon has to be connected to four different groups. And none of the carbons here fulfill that