Double Bonds in Rings

[The8]

Do these not count as stereocenters or do they when not conjugated. My gut says they do because it is plausible to have trans ring structures even though they may be hindered, so they still count as possible stereocenters. ANYONE have anything to say?

Thanks

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[aldol16]

It's more complicated than simple cis- and trans-forms. Take a look at a cyclooctene example here: http://chemistry.stackexchange.com/questions/30940/cis-trans-stability-of-cycloalkenes

 

[laczlacylaci]

Do these not count as stereocenters or do they when not conjugated. My gut says they do because it is plausible to have trans ring structures even though they may be hindered, so they still count as possible stereocenters. ANYONE have anything to say?

Thanks

I always thought for a carbon to be a stereocenter, you need four different things to be bonded to it (to get a stereo difference). So any carbon with a double bond to it, or anything other than sp3 is not considered a stereocenter. Correct if I'm wrong, I may be forgetting something.

 

[Kpw101]

I always though to be a stereocenter, you need four different things to be bonded to it (to get a stereo difference). So any carbon with a double bond to it, or anything other than sp3 is not considered a stereocenter. Correct if I'm wrong, I may be forgetting something.

That's what I always thought too. Thought Cis/Trans or E/Z configurations at double bonds were not really considered to be at stereocenters but they are stereoisomers.

 

[laczlacylaci]

Yes, I am pretty sure that any carbon with a pi bond is not considered a stereocenter, because it defeats the 'stereo' in that word.

 

[The8]

Your wrong, section banks literally from AAMC has a problem about stereocenters and includes double bonds....

 

[Kpw101]

Your wrong, section banks literally from AAMC has a problem about stereocenters and includes double bonds....

Yeah you're right. I looked it up cause I was curious and the definition of a stereocenter is a site where the arrangement of atoms can lead to different stereoisomers, including atoms of double bonds.

 

[laczlacylaci]

Yeah you're right. I looked it up cause I was curious and the definition of a stereocenter is a site where the arrangement of atoms can lead to different stereoisomers, including atoms of double bonds.

Examples?

 

[aldol16]

Examples?

http://www.chem.ucla.edu/~harding/tutorials/stereochem/id_stereocenter.pdf

People are confusing stereocenters with chirality.

 

[laczlacylaci]

http://www.chem.ucla.edu/~harding/tutorials/stereochem/id_stereocenter.pdf

People are confusing stereocenters with chirality.

Ah, thank you so much. My ochem knowledge has been a joke then.

So as for double bonds, the 4 atoms connected to both sides of the bond needs to be different.
And anything that can expand it's octet with a carbonyl connected to four different atoms is a stereocenter? What's the rule for that?

 

[aldol16]

And anything that can expand it's octet with a carbonyl connected to four different atoms is a stereocenter? What's the rule for that?

If all the substituents are different and different stereoisomers are non-superimposable, then you have a stereocenter. But that's way more information than is required for the MCAT. You won't see something like that. For MCAT purposes, they'll mainly ask you about sp3 carbons - don't sweat the details.