Aug 15, 2015
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Pre-Medical
I found this odd question in the KA practice questions, and was wondering if anyone understands it: I thought there were 4 stereogenic centers, but apparently there's one, and I don't understand their explanation.


Thanks in advance!!

Screen Shot 2015-09-08 at 5.31.08 PM.png Screen Shot 2015-09-08 at 5.31.27 PM.png Screen Shot 2015-09-08 at 5.31.08 PM.png Screen Shot 2015-09-08 at 5.31.36 PM.png
 

popopopop

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Dec 18, 2011
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http://csi.chemie.tu-darmstadt.de/ak/immel/script/redirect.cgi?filename=http://csi.chemie.tu-darmstadt.de/ak/immel/tutorials/chirality/

"As derived above, the formal maximum number of stereoisomers (see abvoe 'Chiral Compounds') would be Nmax = 24 = 16. However, in this case only two stereoisomers actually exist, as the steric strain and geometrical limitations of the adamantane resdiue require all substituent to point towards the outside of the molecule (in fact, once the first stereocenter is defined, the remaining three are determined by their relative configuration, and thus the number of observed stereoisomers is 2)."

One explanation stateed the stereocenter is in the "center" of the atom, and not necessarily on the atom itself. I wouldn't be so worried about this problem, looks like an exception that won't be tested on.
 
OP
J
Aug 15, 2015
12
1
Status
Pre-Medical
thanks! weird that they asked that as a practice question..
 

popopopop

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Dec 18, 2011
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Yeah, it's crazy. I kind of understand what it's saying, but I've never heard of this exception to the definition of stereocenters before. If you look up the definition of stereocenters on wiki, it says

"A stereocenter or stereogenic center is an atom bearing groups such that an interchanging of any two groups leads to a stereoisomer."

So I guess the compound in the example fits the bill for not having 2^n stereocenters lol.