The compound shown below has selected carbons labeled. Where are the two stereocenters, with one in the S configuration and the other in the R configuration, located?

Question

The compound shown below has selected carbons labeled.  Where are the two stereocenters, with one in the S configuration and the other in the R configuration, located?

Quizplus · Accepted Answer

11ecba2d_12a7_4793_a3bf_ef03f514e3bd_MD0008_00 A chiral carbon is a carbon with four different substituents. The R or S configuration (stereochemistry) of the stereocenter depends on the spatial arrangement of the substituents. To determine R/S configuration: The priority of substituents attached to the chiral carbon is assigned, with higher priority given to atoms with greater atomic number. In case of a priority tie, the atomic numbers of the next attached atoms are considered. The circular arrangement of groups 1, 2, and 3 is examined. If the lowest-priority group (4) is pointing into the plane (dash), a clockwise circle formed by these groups is R and a counterclockwise circle is S. If the lowest-priority group is pointing out of the plane (wedge), a clockwise circle is S and a counterclockwise circle is R. Carbons 3 and 5 are chiral because each has four different substituents. The priority of the substituents on C3 and C5 is, from highest to lowest (1-4): Cl, CH(OH)CH(CH₂CH₃)Cl, CH₂CH₃, and H. Priorities 1-2-3 are arranged in a clockwise fashion for both carbons, but the lowest-priority group (H) is pointed into the plane on C3 and out of the plane on C5. Therefore, C3 is in the R configuration, whereas C5 is in the S configuration. (Choices A and D) C4 is not chiral because it does not contain four different substituents. It is connected to CH(Cl)CH₂CH₃ on both sides, making the compound symmetrical. (Choice B) The R and S assignments of C3 and C5 are incorrectly reversed. Educational objective: The R or S configuration of a chiral carbon depends on the spatial arrangement of its substituents. When the lowest-priority group is pointed into the plane (dash), the chiral carbon is R if priorities 1-2-3 are arranged in a clockwise fashion and S if they are counterclockwise. When the lowest-priority group is pointed out of the plane (wedge), the chiral carbon is S if priorities 1-2-3 are arranged in a clockwise fashion and R if they are counterclockwise.

The Compound Shown Below Has Selected Carbons Labeled