Stereogenic configurations of Penicillin

[arc5005]

What are the respective absolute configurations of the three stereogenic carbons in penicillin?


Image of penicillin Below:
https://upload.wikimedia.org/wikipe...cillin_core.svg/512px-Penicillin_core.svg.png

A. R, R, R
B. R, R, S
C. S, S, R
D. S, S, S


What's your take on this question?







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TBR Answer: A: R, R, R.


however, a friend and I were looking at this question, and the third stereogenic center is attached to a N (1), then attached to 2 carbons, 1 carbons (SCC), and another carbon (OOO)... They say it has a R configuration, but doesn't the S outbeat the O, which would make the configuration S?

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[PhilzCoffeeAddict]

Maybe its just me, but I can't see the image...

 

[Altius Premier Tutor]

What are the respective absolute configurations of the three stereogenic carbons in penicillin?


Image of penicillin Below:
https://upload.wikimedia.org/wikipe...cillin_core.svg/512px-Penicillin_core.svg.png

A. R, R, R
B. R, R, S
C. S, S, R
D. S, S, S


What's your take on this question?







----------------------------------------------------------------------------------

TBR Answer: A: R, R, R.


however, a friend and I were looking at this question, and the third stereogenic center is attached to a N (1), then attached to 2 carbons, 1 carbons (SCC), and another carbon (OOO)... They say it has a R configuration, but doesn't the S outbeat the O, which would make the configuration S?

Hi @arc5005, I am a current tutor and took the MCAT last June. I think your reasoning is correct and also believe that the third stereogenic center should be S and not R.

 

[AdaptPrep]

Hi, ARC5005.

I agree; it should be R, R, S. The third stereogenic carbon looks like it is R, but the "d" (lowest priority hydrogen) is not pointing backwards. They probably forgot to invert their answer. Your reasoning is correct that a sulfur-bonded carbon has higher priority over an oxygen-bonded carbon (no matter how many oxygen atoms are bonded to it).