5.3 Chirality And The R/S Naming System – Organic Chemistry I

Home » What Is R Organic Chemistry » 5.3 Chirality And The R/S Naming System – Organic Chemistry I

Maybe your like

Let’s take the following molecule as an example to practice the rule:

C in the center and Cl, OH,H, & CH3 around

Step 1: The priorities are assigned.

Cl (1), OH (2), CH3 (3), & H (4)

Step 2: Re-orient the molecule, so H (#4, lowest priority) is in the position away from us. Then, the other three groups will be arranged in this way:

Cl (1) then OH (2), then CH3 (3)

Step 3: Go along the direction from #1→#2→#3; it is in the clockwise direction, so this enantiomer is assigned an R configuration, and the complete name of the molecule is (R)-1-chloroethanol.

Now, let’s assign the configuration of the other enantiomer:

""

Following the same steps, put H away from us, and the arrangement of the other three groups is:

""

The counterclockwise direction gives the S configuration, and the complete name of the molecule is (S)-1-chloroethanol.

1.

C center, CH3, F, H, & CH2CH2Cl around

Solution:

Clockwise (R- configuration)

2.

C center in clockwise direction H, CH2OH, HOOC, Cl

Solution:

Clockwise (R-configuration)

More practical hints about R/S assignment with the Cahn-Ingold-Prelog rule:

  • Assigning priority is the first possible challenge for applying the C.I.P. rule. Review and practice the guidelines in section 5.2.
  • The second challenge is to re-orient the molecule (to arrange the #4 group away from you). The molecule model will be very helpful for this purpose. Assemble a molecular model with four different colors connected to the carbon. Compare your model to the given structure and match the assigned priority to each color; for example, red is #1, blue is #2, etc. Then, rotate the model to arrange the lowest (#4) group away from you and see how the other groups are located to get the answer.

For the perspective formula of enantiomers, it is important to know the following properties:

Tag » What Is R Organic Chemistry