Question

The absolute configuration of

A.(2S, 3R)
B.(2S, 3S)
C.(2R, 3R)
D.(2R, 3S)

Answer 1

Hint: The absolute configuration is determined by R and S. We need to give the priorities, Based on the highest atomic number rule. According to the clockwise and anticlockwise direction we can determine the R and S configuration.

Complete step by step answer:
There are certain rules for determining the configuration of a carbon. First of all we need to specify the priorities of the carbon whose configuration is to be determined. The atom attached with carbon with the highest atomic number will be given first priority. If the first attachment comes out to be the same then we go for the second attachment and then again look for the highest atomic number.
The first priority will be given to the hydroxide group because of the high atomic number of oxygen. If we see for the second group both side carbon is attached so will go to the next attachment. The second priority will go to carbon on which chlorine is attached than in the carboxylic acid group where oxygen is the second attachment. The third priority will be given to the carboxylic acid group and forth to the hydrogen group.

If the first priority lies on the horizontal axis and the rotation of 1, 2 and 3 group is clockwise then the configuration will be S. Hence, there will be S configuration on the carbon number 2.
Similarly we will give priorities to the carbon number 3. The rotation is anticlockwise and hence the configuration will be R.

The correct option is (2S, 3R) that is option A.

Note:
R and S are the nomenclature for a chiral carbon. A chiral carbon is that carbon which has four different groups. The presence of the chiral center makes a molecule stereo active molecules or optically active molecules.