Question

why is this S??

isnt the H the first and Ch3 the second so goes clockwise which make this R??

HACHA CAH

Answer 1

Higher atomic mass species gets priority such as 1st is given to CN because in CN Carbon in directly attached to the nitrogen by three bonds.every bond count as a particular nitrogen atom.in case of methyl(CH_{​​​​​3}​​​​) the carbon is attach to 3 hydrogen atom which has lower atomic mass than nitrogen and in case of ethyl(CH_​​​3CH2) the first carbon is attach to two hydrogen and one carbon both have less atomic mass than nitrogen.In all three species the Carbon is same so we go to more substitution.

OBH CH₂ CH3 H

2nd is assigned to ethyl group because one carbon is attach to it which has higher atomic number than hydrogen of methyl group.

3rd is assigned to methyl group because carbon in methyl group has higher atomic number than hydrogen which is directly attach.

4th is given to hydrogen because it has lowest atomic number among all substitute.

So it forms anticlockwise circle hence it is S configuration

Remember for clockwise circle R configuration is assign and for anticlockwise S configuration is assign