Chemistry and Physics Strategy and Practice

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Chemistry and Physics Strategy and Practice

Post by Lionroar » Tue Oct 17, 2017 4:19 pm

In the book Chemistry and Physics Strategy and Practice, on page 25, question 25 asks about assigning priority to determine R/S configuration. The answer says that the carbon not in the ring gets 1st priority, because it is attached to two other carbons. But I thought that if two atoms attached to a chiral carbon are the same, one should go to the next atom on each chain. Wouldn't the carbon on the chain containing the oxygen get 1st priority, since oxygen has a higher atomic number?
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Re: Chemistry and Physics Strategy and Practice

Post by NS_Tutor_Andrew » Wed Oct 18, 2017 9:36 am

Hi Lionroar,

Thanks for the question! The idea here is that the first carbon in the non-ring substituent of the chiral carbon has a C=C double bond, which "counts" as being bonded to two carbon atoms according to the Cahn-Ingold-Prelog priority rules. For more details, check out the corresponding section of the Wikipedia article on priority. I do agree that the explanation could have presented this more clearly, so we'll make a note of it for future editions.

Hope this helps & best of luck!
Andrew D.
Content Manager, Next Step Test Prep.
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