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Topic: Drawing double bonds  (Read 2501 times)

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Offline PoetryInMotion

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Drawing double bonds
« on: April 17, 2013, 01:53:42 PM »
Odd question perhaps, but which of the following structural formulas are the most correct one? I have not been able to find any nomenclature rules surrounding double bonds and I have also tried to go through Clayden and other well known literature, but I find it hard to see any real patterns. Perhaps someone here knows?


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Offline discodermolide

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Re: Drawing Dubblebonds
« Reply #1 on: April 17, 2013, 02:01:06 PM »
The molecules you have drawn look all the same to me. If you take a C=C tetra substituted, for example:
[H]/C(Cl)=C(C1=CC=CC=C1)/CO

The priority of groups , in order to assign the E or Z configuration follows the well known Cahn-Ingold-Prelog rules.
So the molecule I drew is (Z)-3-chloro-2-phenylprop-2-en-1-ol
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Offline PoetryInMotion

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Re: Drawing double bonds
« Reply #2 on: April 17, 2013, 02:06:39 PM »
Thank you for the answer, but what I am wondering about are the red double bonds in the following image. What is the correct way to draw them?

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Offline discodermolide

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Re: Drawing double bonds
« Reply #3 on: April 17, 2013, 02:16:22 PM »
All are correct, they are just different representations of the same thing. So it does not matter. In ChemDraw, if you draw the C=C and then click on the C=C one of the bonds moves from right to left, click again and it is in the middle, click again and it is back on the right side.
So it does not matter.

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Offline Dan

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Re: Drawing double bonds
« Reply #4 on: April 18, 2013, 03:45:37 AM »
They're all correct, but I would use the second one because I think looks nicer.
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Offline DrCMS

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Re: Drawing double bonds
« Reply #5 on: April 18, 2013, 04:09:13 AM »
I'm with Dan on this aesthetically the 2nd set of bonds look "better" to me.

Offline PoetryInMotion

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Re: Drawing double bonds
« Reply #6 on: April 18, 2013, 01:11:43 PM »
I see. Thank you very much, all of you. And yes, I agree with you on number two being aesthetically better-looking.
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Offline Arkcon

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Re: Drawing double bonds
« Reply #7 on: April 18, 2013, 01:24:47 PM »
I actually like the first one, although the second one is more common.  It looks to me like, almost, the second one is implying -- if not actually true -- that the unsaturations are trans, while the last two are two different ways for drawing cis.  Maybe, if its not important to show that, then the first one should be the choice to remove all possible ambiguity.
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