Question

The absolute configuration of the compound is:

Answer 1

Hint: Suppose there are two test tubes, one containing (-) lactic acid and the other one has (+) enantiomers. How can you distinguish them? To generate a proper model to answer this dilemma, Rosanoff proposed that one compound be chosen as a standard and a configuration arbitrarily assigned to it.

Complete step-by-step answer:
- R- and S- notation use the CIP priority rules for the assignment of the absolute configuration around a stereocenter.
- First, assign priorities as described above to each bonded group surrounding the stereocenter (1, highest to 4, lowest) .
- Second, point the lowest priority (4) atom away from you. Follow the direction of the remaining 3 priorities from highest to lowest priority (lowest to highest number, 1<2<3).
- A counterclockwise direction is an S (sinister, Latin for left) configuration. A clockwise direction is an R (rectus, Latin for right) configuration.

R-S system RULES OF PRIORITY ORDER:
(1) According to the atomic number when only atoms are present and in a group the direct attached atom is considered with the atomic number.
(2) When two or more groups have similar first atoms, the priority is determined by considering the atomic number of the second atom.
(3) If the first atom of two same groups have the same substitutes of higher no will get more priority.
(4) More atomic numbers containing atoms and how many atoms are present of the higher atomic number containing elements.

Now, let us come to the compound given to us:
S→R
as H is in front
S→R
as H is in front we reverse the configuration obtained

Note: Always find out the stereoisomers and then the chiral carbon. Then start using the CIP rule to assign R and S.