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I need help with question (d). I labeled the O the first priority, then the C that's bonded to an O the 2nd, and the C above that is attached to 3 other C's the 3rd priority. So, I ended up getting S, but because the 4th priority was not in the back of the plane, I switched it to R. However, this was not the correct answer, as the answer key told me it is actually S.

I'm confused on how to find R or S in this specific type of situation where there are 3 bonds in the plane and 1 bond coming out. Would appreciate help and pointers on where I went wrong. enter image description here

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  • $\begingroup$ Imagine that the bond coming out is actually in the back. That would change the configuration. Now switch the places between OH and the 4th priority. That would change the configuration again. $\endgroup$
    – Ivan Neretin
    Commented Jun 10, 2021 at 8:25
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    $\begingroup$ Build a 3D model if you can't see the structure around the centre in your head. BTW it is not by any stretch in the plane. $\endgroup$
    – matt_black
    Commented Jun 10, 2021 at 10:10
  • $\begingroup$ Recognize that carbon "e" lies below the cyclohexene ring. This post may be of help. chemistry.stackexchange.com/questions/151831/… $\endgroup$
    – user55119
    Commented Jun 17, 2021 at 2:12

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You can also assign based on the highest priority. After assigning all priorities, if the highest priority group is forward and the direction from 1->2->3 is clockwise, the configuration is R. If counterclockwise, the configuration is S.

In this case, the absolute configuration of d is straightforward. You do not switch from S to R because the low priority is not backward. You keep it as S because the highest priority is facing forward.

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