Among the following groups, what is the correct order of priorities in the R,S system?
A) (i) (ii) (iii) (iv)
B) (ii) (i) (iv) (iii)
C) (iv) (ii) (i) (iii)
D) (ii) (iv) (i) (iii)

Question

Among the following groups, what is the correct order of priorities in the R,S system? 
A) (i) > (ii) > (iii) > (iv) 
B) (ii) > (i) > (iv) > (iii) 
C) (iv) > (ii) > (i) > (iii) 
D) (ii) > (iv) > (i) > (iii)

Quizplus · Accepted Answer

The correct order of priorities in the R,S system is determined by assigning priority based on the atomic number of the substituent attached to the stereocenter. Hence, the correct order of priorities in the R,S system is (i) > (iii) > (ii) > (iv), because the substituents on carbon 1 and carbon 3 both have higher atomic numbers than the substituent on carbon 2, and the substituent on carbon 4 has the lowest atomic number of all. However, the R/S designation is based on the opposite order of priorities (lowest to highest), so the R/S designation of this molecule would be (S)-4-chloro-3-ethyl-1-methylcyclohexene. Thus, option D is the best choice.

Among the Following Groups, What Is the Correct Order of Priorities