Skip to main content
Ch. 4 - Isomers: The Arrangement of Atoms in Space
Bruice - Organic Chemistry 8th Edition
Bruice8th EditionOrganic ChemistryISBN: 9780135213711Not the one you use?Change textbook
Chapter 5, Problem 68c

Name the following compounds using R,S designations:
c. Structural formula of a molecule showing substituents for R and S configuration designation.

Verified step by step guidance
1
Step 1: Identify the chiral centers in the molecule. A chiral center is a carbon atom bonded to four different groups. In the given structure, there are two chiral centers: the carbon bonded to Cl, H, CH3, and the other carbon, and the carbon bonded to OH, H, CH2CH3, and the other carbon.
Step 2: Assign priorities to the substituents attached to each chiral center based on the Cahn-Ingold-Prelog priority rules. The priority is determined by the atomic number of the atoms directly attached to the chiral center. For example, Cl has the highest priority (atomic number 17), followed by CH3, and then H for the first chiral center.
Step 3: Orient the molecule so that the lowest priority group (usually H) is pointing away from you. This is important for determining the R or S configuration. For the first chiral center, ensure H is pointing away from your view.
Step 4: Determine the order of the remaining substituents (1 → 2 → 3) in a clockwise or counterclockwise direction. If the order is clockwise, the configuration is R. If counterclockwise, the configuration is S. Repeat this process for the second chiral center.
Step 5: Combine the R,S designations for both chiral centers into the name of the compound. For example, if the first chiral center is R and the second is S, the compound would be named with the R,S designations included.

Verified video answer for a similar problem:

This video solution was recommended by our tutors as helpful for the problem above.
Video duration:
6m
Was this helpful?

Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

Chirality

Chirality refers to the geometric property of a molecule that makes it non-superimposable on its mirror image. A chiral molecule typically has a carbon atom bonded to four different substituents, leading to two distinct configurations known as enantiomers. Understanding chirality is essential for naming compounds using R,S designations, as it determines the spatial arrangement of atoms.
Recommended video:
Guided course
05:10
What is chirality?

R,S Nomenclature

R,S nomenclature is a system used to assign configurations to chiral centers in organic molecules. The 'R' (rectus) and 'S' (sinister) designations are determined by the Cahn-Ingold-Prelog priority rules, which rank substituents based on atomic number and connectivity. This systematic approach allows chemists to clearly communicate the specific 3D arrangement of atoms in chiral compounds.
Recommended video:
Guided course
03:07
R and S Naming- Step 4

Cahn-Ingold-Prelog Priority Rules

The Cahn-Ingold-Prelog priority rules are a set of guidelines used to assign priority to substituents attached to a chiral center. According to these rules, higher atomic numbers take precedence over lower ones, and if two atoms are the same, the next atoms in the chain are considered. This ranking is crucial for determining the R or S configuration of a chiral compound, as it influences the final designation.
Recommended video:
Guided course
01:48
Why stereoisomers need their own naming system.