Arrange the following groups in the order of increasing priority according to the Cahn-Ingold-Prelog Rules (lowest priority to highest priority) .

Question

Arrange the following groups in the order of increasing priority according to the Cahn-Ingold-Prelog Rules (lowest priority to highest priority).

Quizplus · Accepted Answer

According to the Cahn-Ingold-Prelog Rules, the priority is determined based on the atomic number of the substituents attached to a stereocenter. The group with the lowest atomic number has the lowest priority, while the group with the highest atomic number has the highest priority. 
In the given structure, the four groups attached to the stereocenter are: 
I - CH3, II - CH2CH2OH, III - C6H5, IV - Cl. 
The atomic numbers of the substituents are: H (1), C (6), O (8), and Cl (17). Therefore, the group with Cl (IV) has the highest priority and the group with CH3 (I) has the lowest priority. 
Thus, the correct order of priority is III, I, IV, II, which is given only in choice C.

Arrange the Following Groups in the Order of Increasing Priority