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Topic: R or S ? for fun (Movies)  (Read 10030 times)

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laotree

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R or S ? for fun (Movies)
« on: August 26, 2005, 11:46:08 PM »
R or S

Memy

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Re:R or S ? for fun (Movies)
« Reply #1 on: August 27, 2005, 02:47:15 AM »
There are no stereogenic centres in these two molecules ( stereogenic centre = tetrahedral carbon atom to which four different substituents are attached). Therefore, it is pointless to talk of R and S configuration.

However, the two molecules are chiral , i.e. not superimposable to their mirror images.
« Last Edit: August 27, 2005, 02:48:47 AM by Memy »

Offline Mitch

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Re:R or S ? for fun (Movies)
« Reply #2 on: August 27, 2005, 03:26:57 AM »
Incorrect, the second structure is R.
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Re:R or S ? for fun (Movies)
« Reply #3 on: August 27, 2005, 03:49:11 AM »
Incorrect, the second structure is R.

Yup.  Although some people prefer to use different notation for things with an axis of chirality but not a chiral center.  R/S is still probably the most common.

And the first one does have a chiral center.  It's R.  The Z-double bond is higher priority by the CIP system.

Also, stereogenic centers aren't only chiral carbon atoms, the carbons of alkenes can be stereogenic too since the alkene can be E or Z.

laotree

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Re:R or S ? for fun (Movies)
« Reply #4 on: August 27, 2005, 06:59:46 AM »
These two are someting easy to ignore or misunderstand for newcomers in organic chemistry.

The first one movies is right. The second one is aixal chiral, could be named by R/S or M/P. There are a lot aixal chirality exist in organic and natural product chemistry, not limited in biphenyl ring!

Offline Winga

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Re:R or S ? for fun (Movies)
« Reply #5 on: August 28, 2005, 12:49:58 PM »
How to determine R/S configuration to the 2nd structure?

Z has a higher priority, then, how about R & S?

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Re:R or S ? for fun (Movies)
« Reply #6 on: August 28, 2005, 01:20:07 PM »
How to determine R/S configuration to the 2nd structure?

Z has a higher priority, then, how about R & S?

Same way as usual.  The Z alkene has 1st priority, the E alkene is second, the methyl is third.

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Re:R or S ? for fun (Movies)
« Reply #7 on: August 28, 2005, 01:42:29 PM »
For the second structure look down the longest side of the molecule. Look at the attachments sticking out on the sides and see if they're attachments are attached spirally clockwise or counter-clockwise. Clockwise will give you R and counterclockwise will give you S.
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Offline Winga

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Re:R or S ? for fun (Movies)
« Reply #8 on: August 28, 2005, 04:17:29 PM »
For the second structure look down the longest side of the molecule. Look at the attachments sticking out on the sides and see if they're attachments are attached spirally clockwise or counter-clockwise. Clockwise will give you R and counterclockwise will give you S.
Did I illustrate it correctly?

1. Look at the molecule from the axis shown by the figure or from opposite side.
2. Assign the highest priority to the substituent (isopropyl group) which is closest to us.
3. If the substituents are attached spirally clockwise according to priority, then it is (R) configuration.

Am I right?

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Re:R or S ? for fun (Movies)
« Reply #9 on: August 29, 2005, 12:10:50 AM »
perfect
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Offline Winga

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Re:R or S ? for fun (Movies)
« Reply #10 on: August 29, 2005, 01:48:20 AM »
Same way as usual.  The Z alkene has 1st priority, the E alkene is second, the methyl is third.
About the 2nd question, I mean when two of the substituents which are R/S relationship to each other, which one has a higher priority, R or S?

Blueshawk

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Re:R or S ? for fun (Movies)
« Reply #11 on: August 29, 2005, 09:07:50 AM »
From Winga's illustration....

Why is 1st substituent a higher priority group than 2nd substituent???

They look the same to me, they are both propal groups???

Or does it have to due with the orientation of those groups when looking down the line of sight in Winga's drawing???

This is the part I dont like about Organic...it is hard to picture, But a nice illustration by Winga..

Winga------>  What program did you draw that with???

Offline Winga

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Re:R or S ? for fun (Movies)
« Reply #12 on: August 29, 2005, 12:47:52 PM »
From Winga's illustration....

Why is 1st substituent a higher priority group than 2nd substituent???

They look the same to me, they are both propal groups???

Or does it have to due with the orientation of those groups when looking down the line of sight in Winga's drawing???

This is the part I dont like about Organic...it is hard to picture, But a nice illustration by Winga..

Winga------>  What program did you draw that with???
About the priority of substituents, I illustrated that the one closer to our eyes will have a higher priority.

I used ChemDraw to draw the organic molecules and edited it by Macromedia Flash.

Offline Winga

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Re:R or S ? for fun (Movies)
« Reply #13 on: August 29, 2005, 12:52:07 PM »
Could someone describe about M/P configuration?

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Re:R or S ? for fun (Movies)
« Reply #14 on: August 29, 2005, 01:44:41 PM »
Winga, do you have an example of where you would have to pick between an R and an S sidechain?  I'm trying to think of an example where the compound wouldn't be meso because of a plane of symmetry.

Could someone describe about M/P configuration?

M is like R, P is like S.  For axial chirality you also sometimes see aR and aS instead of just R and S.

With respect to Blueshawk's question, Winga is correct.  The substituents on the "front" ring are automatically given higher priority than those on the "back" ring.  So, the isopropyl groups are priority 1 and 3, respectively.  The H atoms on the other side of the rings are 2 and 4, respectively.

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