Question

In case of R - S configuration the group having highest priority is ?
A. \[-N{{O}_{2}}\]
B. \[-N{{H}_{2}}\]
C. \[-CN\]
D. \[-OH\]

Answer 1

Hint: We have to give numbers to all the substituents that are attached to carbon while determining the R - S configuration of the molecule. The numbering to substituents is supposed to be given in a manner of their priorities. Higher is the atomic number of the atom that is attached to carbon, higher is its priority means lower its number.

Complete step by step answer:
The given substituents or functional groups in the question are nitro (\[-N{{O}_{2}}\]), amine (\[-N{{H}_{2}}\]), cyanide (\[-CN\]), and alcohol or hydroxide (\[-OH\]).
The nitro group is attached to carbon through nitrogen, the amine group attached to carbon through nitrogen, the cyanide group attached to carbon through carbon and the alcohol group attached to carbon through oxygen.
So, we have to give first number or highest priority to alcohol because among all the given options the atomic number of oxygen is high when compared to nitrogen and carbon.
The atomic number of oxygen is 8, the atomic number of nitrogen is 7 and the atomic number of carbon is 6.
In case of R, S configuration the group having highest priority is \[-OH\].

So, the correct option is D.

Note: R, S nomenclature was given by Cahn, Ingold and Prelog in 1956. It is also called the CIP rule. The four groups or substituents that are attached to the chiral carbon are ranked in order of priority by using atomic numbers.
R-rector
S-sinister