Chapter 5, Problem 39P

Interpretation Introduction

(a)

Interpretation: The stereogenic centers in the ball-and-stick model of ezetimibe are to be located.

Concept introduction: A carbon atom that has four nonequivalent atoms or groups attached to it is known as chiral carbon atom. Chiral carbon centers are also called as asymmetric or stereogenic centers.

Answer to Problem 39P

The stereogenic centers in ezetimibe are,

Explanation of Solution

The given ball-and-stick model of ezetimibe is shown below.

Figure 1

In the ball-and-stick model of ezetimibe, yellow balls represent halogen atom as they contain one covalent bond. Black balls are bonded to each other through four covalent bonds, thus; they represent carbon atom. Red balls represent oxygen atom as they contain two covalent bonds and blue balls represent nitrogen atom because they contain three covalent bonds.

The stereogenic center is one that has four different groups attached to carbon atom tetrahedrally. The stereogenic centers in the given molecule are located by omitting all ${\text{CH}}_{\text{2}}$ and ${\text{CH}}_{\text{3}}$ groups and all $s{p}^2$ hybridized carbon atoms. The stereogenic centers in ezetimibe are shown below which are marked by asterisk. For easy reference, the ball-and-stick model of ezetimibe is represented as follows,

Figure 2

There are three stereogenic centers present in ezetimibe.

Conclusion

There are three stereogenic centers present in ezetimibe.

Interpretation Introduction

(b)

Interpretation: Each stereogenic center in ezetimibe are to be labeled as $R$ or $S$.

Concept introduction: A carbon atom that has four nonequivalent atoms or groups attached to it is known as chiral carbon atom. Chiral carbon centers are also called as asymmetric or stereogenic centers.

The naming of chiral center and geometric isomers are based on Cahn-Ingold-Prelog priority rules. If the priority assigned to each group attached to the chirality center in a molecule is in a clockwise direction, then it is the R-stereoisomer, and if this is counter-clockwise, then it is the S-stereoisomer. R and S-stereoisomer are mirror images of each other.

Answer to Problem 39P

The $R$ or $S$ configuration of each stereogenic center in ezetimibe are shown below

Explanation of Solution

The $R$ or $S$ configuration of each stereogenic center in ezetimibe are shown below.

Figure 3

The stereogenic center (1) has $S$ configuration because the rotation is clock-wise and least priority group is above the plane. The stereogenic center (2) has anti-clock wise rotation and least priority group is above the plane. Therefore, it has $R$ configuration. The stereogenic center (3) has anti-clock wise rotation and least priority group is below the plane. Therefore, it has $S$ configuration.

Conclusion

In ezetimibe, one of the stereogenic centers has $R$ configuration and the other two possess $S$ configuration.