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Chemistry Forums for Students => Organic Chemistry Forum => Topic started by: sharbeldam on November 16, 2019, 05:24:34 AM

Title: Is this okay?
Post by: sharbeldam on November 16, 2019, 05:24:34 AM

I'm new O-chem 1 tutor in my school and i have been asked this, I think the answer is yes but I'm not sure.
If the 4th priority in a cyclic compound is part of the cycle and the student does not want to use models to figure out the configuration, is it okay to dissect the cycle into 1 chain compound and make the 4th priority inwards? like the example below in the picture, i think it would make my question clearer.

Title: Re: Is this okay?
Post by: AWK on November 16, 2019, 08:11:48 AM

After (correct) assigning priorities, you forget about the existence of the molecule. You work on the priorities surrounding the chiral atom.

Title: Re: Is this okay?
Post by: sharbeldam on November 16, 2019, 08:43:33 AM

I dont understand what you said.

Title: Re: Is this okay?
Post by: AWK on November 16, 2019, 09:37:09 AM

After assigning priorities to substituents, the chain or ring is no longer relevant. You operate on priorities and using the logic of actions with priorities you decide on the configuration.

Title: Re: Is this okay?
Post by: sharbeldam on November 16, 2019, 10:27:15 AM

So what I've done in this picture is acceptable? Can I get a yes or no :D
 since in O-chem 1 as you know for sure the 4th priority should be inwards to solve on paper (without models).
and the ring bond isnt rotatable like the chain so i guess the question is legit.

Title: Re: Is this okay?
Post by: AWK on November 16, 2019, 10:48:38 AM

The result is correct (I haven't criticized it after all), but the argument is pulled.

Title: Re: Is this okay?
Post by: Babcock_Hall on November 16, 2019, 03:46:12 PM

You can draw a carbon with the labels 1, 2, 3, and 4 on it.  Then you can rotate the labels using certain guidelines to move the lowest priority group to the rear.

Title: Re: Is this okay?
Post by: sharbeldam on November 16, 2019, 05:14:41 PM

So basically what I did no? i need to know for sure if that way in the picture is applicable and can be done, cause it makes it all much easier

Title: Re: Is this okay?
Post by: AWK on November 16, 2019, 06:01:50 PM

Everything is fine. Babcock_Hall wrote exactly the same as me (in slightly better English).
When we assign priorities to substituents we are no longer dealing with a specific molecule, but with its model prepared only to determine the absolute configuration. We can do this by rotating this model according to the appropriate procedure (as you did), or transform this model to a formula in Fischer convention and use only transformations on the plane also correctly determining the absolute configuration.