Question

What is the configuration of each of the following compounds? (R or S) please explain

What is the configuration of each of the following compounds? R configuration S configuration R configuration S configuration R configuration S configuration

Answer 1

In order to assign the configuration as R or S:

(1) Assign the priority (high = 1 to low = 4) to each group attached to the chirality center based on atomic number.

(2) Reposition the molecule so that the lowest priority group is away from you as if you were looking along the C-(4) σ bond. If you are using a model, grasp the lowest priority group in your fist

(3) Determine the relative direction of the priority order of the three higher priority groups (1 to 2 to 3)

(4)If this is clockwise then it is the R-stereoisomer (Latin; rectus = right handed)

(5) If this is counter-clockwise then it is the S-stereoisomer (Latin; sinister = left handed)

(6) If there is more than one stereocenter, then the location needs to be included with the locant, e.g. (2R)

Comming to the given compounds:

Part A:

The order of priority is : (1) -CH₂Br (2) -CH(CH₃)₂ (3) -CH₂CH₃ (4) -CH₃

While giving relative direction it is along the counter-clockwise direction, and the least priority group is away from us so the configuration is (S)

Part B :

The order of priority is : (1) -OH (2) -CH₂OH (3) -CH₂CH₂CH₃ (4) -H

While giving relative direction it is along the counter-clockwise direction, and the least priority group is not away from us so the configuration is reverse of our expectation , therefore the configuration is (R).

Part C :

The order of priority is : (1) -Br (2) -CH₂CH₃ (3) -CH₃ (4) -H

While giving relative direction it is along the clockwise direction, and the least priority group is not away from us so the configuration is reverse of our expectation , therefore the configuration is (S).