Question

heloo friends.....

please tell me what is R,S configuration ?

Answer 1

HELLO THERE!

The R-S configuration is a well-trending method of nomenclature.

R stands for Rectus.

S stands for Sinister.

For this type of configuration, first you need to draw the Fischer Projection of the compound, so that you are able to represent the three dimensional structure on paper. To draw the Fischer projection, keep the carbons in a vertical line.

Now, number the atoms based on their atomic numbers. The atom with highest atomic number gets first priority. Now, rotate your hand from the first priority atom towards the second priority atom. You may have two cases:

=> The rotation direction is clockwise. If so, then the Nomenclature will be R (Rectus).

=> The rotation direction is anticlockwise. If so, then the Nomenclature will be S (Sinister).

Now, if the atom with lowest priority is present in the horizontal line with a carbon atom, then the Nomenclature is reversed.

Like, if a compound has R nomenclature and the atom with lowest priority is present in the horizontal line, then it will be S, and vice versa. Consider an example in the attachment given:

OH gets the highest priority, then COOH, then CH₃, and then H. The lowest priority group H is present in Horizontal line. Rotation direction from OH to COOH is anticlockwise, so nomenclature should have been (S). However, since H is present in horizontal line, it becomes (R).

HOPE THIS HELPS...

Thanks!