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.
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.