Question

What does R configuration mean?

Answer 1

Hint : While naming alkyl halides on the basis of IUPAC nomenclature rule we get name as $2 -$ chlorobutane twice, they are not same compounds but they are known as enantiomers so to write these we need some extra rules at that time R-S configuration comes in picture.

Complete Step By Step Answer:
Talking about R configuration, while denoting it we move clockwise in which we go from higher priority to lower priority.
R-S stereoisomers are the non-superimposable images of each other. It's like our both hands are the same but opposite to each other in orientation.
There are some general rules while denoting R-S configuration: Higher atomic numbers which are directly attached to atoms have higher priority. Atomic number of the atom attached to the one , we consider it in step one if in case there are two same substituents.
Higher the number of the same atom branch, we give greater priority to it. For example, isopropyl will have higher priority than that of ethyl.

Note :
There is a whole different study of stereochemistry which is the study of stereoisomers which have the same molecular formula but when it comes to three-dimensional orientation it is different. In general, R-S configuration is often called as right-hand and left-hand nomenclature.