Question

rank the following substituents from highest to lowest priority according to the cahn - ingold - prelog system.
-ch₃ -cn -ch₂oh -br
i ii iii iv
a. iv>i>iii>ii
b. iii>iv>ii>i
c. ii>i>iii>iv
d. iv>iii>ii>i

Explanation:

Step1: Recall CIP rule

Priority is based on atomic number of the first - atom attached to the chiral center.

Step2: Identify first - atoms

For - CH₃, first - atom is C (atomic number = 6); for - CN, first - atom is C (atomic number = 6); for - CH₂OH, first - atom is C (atomic number = 6); for - Br, first - atom is Br (atomic number = 35).

Step3: Break ties

When first - atoms have the same atomic number, look at the atoms attached to the first - atom. For - CN, C is triple - bonded to N (counted as three N atoms); for - CH₂OH, C is bonded to two H and one O; for - CH₃, C is bonded to three H.

Step4: Rank priorities

Br has the highest atomic number, so - Br has the highest priority. Among - CH₂OH, - CN and - CH₃, - CH₂OH has higher priority than - CN (due to O having higher atomic number than N in the second - level atoms) and - CN has higher priority than - CH₃. So the order is - Br > - CH₂OH > - CN > - CH₃, or IV > III > II > I.

Answer:

D. IV > III > II > I