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Topic: Determining Chrial Centers  (Read 5995 times)

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Offline THECapedCaper

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Determining Chrial Centers
« on: October 16, 2012, 12:47:27 PM »
I have a little confusion as to what determines a chiral center in the larger molecules, namely hydrocodone.



As far as I can tell, anything that is a CH2 or CH3 cannot be considered chiral, but do C=O or C=C bonds fall under the same category because they're not bonded to four groups? What are the chiral centers of hydrocodone?

Offline discodermolide

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Re: Determining Chrial Centers
« Reply #1 on: October 16, 2012, 12:51:52 PM »
C=O and C=C bonds cannot be chiral.
In your molecule there seem to be 4 chiral centers.
Simply put the same criteria apply for simple and complex molecules, 4 different substituents and non-superimposable on it's mirror image.
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Offline curiouscat

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Re: Determining Chrial Centers
« Reply #2 on: October 16, 2012, 01:10:42 PM »
C=O and C=C bonds cannot be chiral.
In your molecule there seem to be 4 chiral centers.
Simply put the same criteria apply for simple and complex molecules, 4 different substituents and non-superimposable on it's mirror image.

Silly question: Why isn't this (see below) atom considered chiral? Even accounting for resonance aren't there essentially four different substituents?


Offline THECapedCaper

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Re: Determining Chrial Centers
« Reply #3 on: October 16, 2012, 01:14:18 PM »
So, then these four carbons would be the chiral centers (marked with red stars)?



In that case, we have 16 stereoisomers (2^n) and 14 diasteroisomers (2^n - 2), correct?

Offline discodermolide

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Re: Determining Chrial Centers
« Reply #4 on: October 16, 2012, 01:14:44 PM »
There are not 4 different substituents on that carbon atom. It's part of a phenyl ring. The double bonds are not static as you said.
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Offline discodermolide

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Re: Determining Chrial Centers
« Reply #5 on: October 16, 2012, 01:15:55 PM »
Yes, that is correct.
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Offline curiouscat

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Re: Determining Chrial Centers
« Reply #6 on: October 16, 2012, 01:18:42 PM »
There are not 4 different substituents on that carbon atom. It's part of a phenyl ring. The double bonds are not static as you said.

I see. Thanks!

Would that position (red box) become a Chiral Centre if I, say, brominated it there?  {Bet it can't be done! But who knows! You wizards have all kinds of synthetic magic up you sleeves!  ;D }

Offline discodermolide

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Re: Determining Chrial Centers
« Reply #7 on: October 16, 2012, 01:21:10 PM »
Well assuming you could brominate there then it would give a new chiral centre.
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Offline curiouscat

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Re: Determining Chrial Centers
« Reply #8 on: October 16, 2012, 01:24:02 PM »
Well assuming you could brominate there then it would give a new chiral centre.

Thanks again!

Offline fledarmus

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Re: Determining Chrial Centers
« Reply #9 on: October 16, 2012, 01:35:36 PM »
So, then these four carbons would be the chiral centers (marked with red stars)?



In that case, we have 16 stereoisomers (2^n) and 14 diasteroisomers (2^n - 2), correct?

Not really - build some models. Having ring structures will restrict the total number of possible stereoisomers. You will find that certain combinations of R and S just won't be possible to get the atoms to line up.

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