Assigning R and S configuration always challenging. we are providing a short trick to assign R and S simple configuration. In this method, you don't have to rotate carbon bond

1. Smart tricks to assign R/S configuration without rotating covalent bond
Candidates consider stereochemistry as one of the difficult topics from organic chemistry. Assigning
R/S configuration is one of them. Many methods are available for assign R/S configuration like Cahn,
Ingold and Prelog but this method involves rotation of covalent bond, which many students are not
comfortable with and it is a time consuming method.
Here we are presenting a short and simple method for assign R/S configuration without rotating
bonds. If you study properly you can assign R/S configuration within 5 seconds irrespective of groups.
You don’t have to remember the complete table, just remember one value.
For example if you remember 4F(-), then 3F and 1F will opposite to it i.e. (+), where as 2F will be same
as 4F i.e. (-). Same is true for 4 B.
4F(-) 4B(+)
3F(+) 3B(-)
2F(-) 2B(+)
1F(+) 1B(-)

2. 4F(-) 4B(+)
3F(+) 3B(-)
2F(-) 2B(+)
1F(+) 1B(-)
4 = 4th Position Priority group
F = Front side
B = Back side
-Ve = Change configuration
+Ve = Same configuration
Clockwise = RAnitclockwise = S

3. Assign Priority
Clockwise
11
22
33
44
Example-1
Rule 1 – Assign Priority
Rule-2 Select one group above the plane or below the plane. Do not consider this group
while drawing the ascending order clockwise or anticlockwise curve.
In the above example,
we have to select the 4th priority group which is below the plane(Backside) ( You can
select a third priority group also) and have drawn the clockwise curve.
As per the table 4th priority group is the backside it is 4B(+) and + indicate configuration
should not change its R configuration.
You can also assign using 3rd priority group – it front side it 3F(+) and configuration would
be same R
4F(-) 4B(+)
3F(+) 3B(-)
2F(-) 2B(+)
1F(+) 1B(-)

4. 1
2Assign Priority
3
4
Anti-Clockwise
1
2
3
4
1B(-)
1st Priority group on back side and - sign indicate reverse the configuration hence its R configuration
4F(-) 4B(+)
3F(+) 3B(-)
2F(-) 2B(+)
1F(+) 1B(-)

5. Example -2
Assign Priority
1
2
Anti-Clockwise
3
4
1
2
3
4
1F(+)
1st Priority group on front side and + sign indicate no change in configuration hence its S configuration
4F(-) 4B(+)
3F(+) 3B(-)
2F(-) 2B(+)
1F(+) 1B(-)
You can assign configuration to any chiral molecule without rotating bonds.
Regular practice will help you in attaining mastery in assigning configuration.