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Topic: Axial chirality  (Read 3021 times)

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Offline Rutherford

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Axial chirality
« on: July 30, 2013, 10:43:08 AM »
As I couldn't find any good text about this topic, I have to ask a question:

Why are axial enantiomers represented as this:

but not as in the attached picture?
« Last Edit: July 30, 2013, 11:43:29 AM by Raderford »

Offline Dan

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Re: Axial chirality
« Reply #1 on: July 30, 2013, 02:23:03 PM »
Because they are not planar. If they were planar, as you have drawn, they would not be chiral (mirror plane in the plane of the page). Your representations do not indicate which enantiomer you have.
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Offline Rutherford

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Re: Axial chirality
« Reply #2 on: July 31, 2013, 06:17:19 AM »
I think also that these conformations I drew would be very unstable, because of steric hindrances. Then that's why the true enantiomers can't interconvert easily. How do I know which one is Sa, and which one is Ra?

Offline Dan

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Re: Axial chirality
« Reply #3 on: July 31, 2013, 08:06:03 AM »
R/S assignment example here.
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Offline Rutherford

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Re: Axial chirality
« Reply #4 on: July 31, 2013, 08:47:53 AM »
Ok, thanks.

Offline Rutherford

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Re: Axial chirality
« Reply #5 on: July 31, 2013, 08:53:18 AM »
Why aren't allenes planar as alkenes?

Offline Dan

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Re: Axial chirality
« Reply #6 on: July 31, 2013, 09:07:30 AM »
It's to do with the molecular obitals - you can easily google stuff like this yourself.

e.g. http://bouman.chem.georgetown.edu/S02/lect12/lect12.htm
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Offline Rutherford

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Re: Axial chirality
« Reply #7 on: July 31, 2013, 09:18:23 AM »
Sorry, I tried, but couldn't so easy. Thank you for the help, it is clear now.

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