Chapter 5, Problem 5.61P

Interpretation Introduction

(a)

Interpretation: The relation between the compounds A and B is to be determined.

Concept introduction: Newman projections are drawn to visualize the different conformations of a compound around $\text{C}-\text{C}$ bond. In Newman projection the circle represents the back carbon and the dot represents the front carbon.

The stereochemistry of the compound is determined by prioritizing the groups attached to its stereogenic center. The groups are prioritized on the basis of atomic number of their atoms. The group that contain atom with higher atomic number is given higher priority. Complete the circle in decreasing order of priority from $1\to 2\to 3$. The configuration of the compound is R and S when circle rotates in clockwise and anticlockwise direction.

Answer to Problem 5.61P

Compounds A and B are identical.

Explanation of Solution

The given Newman projection A is,

Figure 1

In Newman projection, the circle represents the back carbon and the dot represents the front carbon. The back carbon is substituted by one hydroxyl, one hydrogen atom and one hydroxymethyl group and the front carbon is substituted by one hydrogen atom, one hydroxyl group and one formyl group. The skeletal structure for the given projection is,

Figure 2

In the given compound, $\text{OH}$, $\text{H}$, $\text{CHO}$ and $\text{C}\left(\text{II}\right)$ groups are attached to $\text{C}\left(\text{I}\right)$. The highest priority group is $\text{OH}$ because the atomic number is higher. The carbon atom of group $\text{CHO}$ is bonded to oxygen atom whereas carbon atom of $\text{C(II)}$ is bonded to three different groups. The prioritization of groups is shown in Figure 2. Hence, the $R$ or $S$ configuration around two stereogenic centers are, $\text{C}\left(\text{I}\right)$ $R$, $\text{C}\left(\text{II}\right)$ $R$.

The given Newman projection B is,

Figure 3

In Newman projection the circle represents the back carbon and the dot represents the front carbon. The back carbon is substituted by one hydroxyl, one hydrogen atom and one hydroxymethyl group and the front carbon is substituted by one hydrogen atom, one hydroxyl group and one formyl group. The skeletal structure for the given projection is,

Figure 4

In the given compound, $\text{OH}$, $\text{H}$, $\text{CHO}$ and $\text{C}\left(\text{II}\right)$ groups are attached to $\text{C}\left(\text{I}\right)$. The highest priority group is $\text{OH}$ because the atomic number is higher. The carbon atom of group $\text{CHO}$ is bonded to oxygen atom whereas carbon atom of $\text{C(II)}$ is bonded to three different groups. The prioritization of groups is shown in Figure 4. Hence, the $R$ or $S$ configuration around two stereogenic centers are, $\text{C}\left(\text{I}\right)$ $R$, $\text{C}\left(\text{II}\right)$ $R$.

Both A and B have same configuration around the stereogenic centers. Hence, compounds A and B are identical.

Conclusion

Compounds A and B are identical.

Interpretation Introduction

(b)

Interpretation: The relation between the compounds A and C is to be determined.

Concept introduction: Newman projections are drawn to visualize the different conformations of a compound around $\text{C}-\text{C}$ bond. In Newman projection the circle represents the back carbon and the dot represents the front carbon.

The stereochemistry of the compound is determined by prioritizing the groups attached to its stereogenic center. The groups are prioritized on the basis of atomic number of their atoms. The group that contain atom with higher atomic number is given higher priority. Complete the circle in decreasing order of priority from $1\to 2\to 3$. The configuration of the compound is R and S when circle rotates in clockwise and anticlockwise direction.

Answer to Problem 5.61P

Compounds A and C are enantiomers.

Explanation of Solution

The given Newman projection A is,

Figure 1

In Newman projection the circle represents the back carbon and the dot represents the front carbon. The back carbon is substituted by one hydroxyl, one hydrogen atom and one hydroxymethyl group and the front carbon is substituted by one hydrogen atom, one hydroxyl group and one formyl group. The skeletal structure for the given projection is,

Figure 2

In the given compound, $\text{OH}$, $\text{H}$, $\text{CHO}$ and $\text{C}\left(\text{II}\right)$ groups are attached to $\text{C}\left(\text{I}\right)$. The highest priority group is $\text{OH}$ because the atomic number is higher. The carbon atom of group $\text{CHO}$ is bonded to oxygen atom whereas carbon atom of $\text{C(II)}$ is bonded to three different groups. The prioritization of groups is shown in Figure 2. Hence, the $R$ or $S$ configuration around two stereogenic centers are, $\text{C}\left(\text{I}\right)$ $R$, $\text{C}\left(\text{II}\right)$ $R$.

The given Newman projection C is,

Figure 5

In Newman projection the circle represents the back carbon and the dot represents the front carbon. The back carbon is substituted by one hydroxyl, one hydrogen atom and one hydroxymethyl group and the front carbon is substituted by one hydrogen atom, one hydroxyl group and one formyl group. The skeletal structure for the given projection is,

Figure 6

In the given compound, $\text{OH}$, $\text{H}$, $\text{CHO}$ and $\text{C}\left(\text{II}\right)$ groups are attached to $\text{C}\left(\text{I}\right)$. The highest priority group is $\text{OH}$ because the atomic number is higher. The carbon atom of group $\text{CHO}$ is bonded to oxygen atom whereas carbon atom of $\text{C(II)}$ is bonded to three different groups. The prioritization of groups is shown in Figure 6. Hence, the $R$ or $S$ configuration around two stereogenic centers are, $\text{C}\left(\text{I}\right)$ $S$, $\text{C}\left(\text{II}\right)$ $S$.

Both A and C have opposite configuration around the stereogenic centers. Hence, compounds A and C are enantiomers.

Conclusion

Compounds A and C are enantiomers.

Interpretation Introduction

(c)

Interpretation: The relation between the compounds A and D is to be determined.

Concept introduction: Newman projections are drawn to visualize the different conformations of a compound around $\text{C}-\text{C}$ bond. In Newman projection the circle represents the back carbon and the dot represents the front carbon.

Enantiomer of a compound has opposite configuration at stereogenic centers. Diastereomers of a compound have at least one stereogenic centre with same configuration and at least one with opposite configuration.

Answer to Problem 5.61P

Compounds A and D are diastereomers.

Explanation of Solution

The given Newman projection A is,

Figure 1

In Newman projection, the circle represents the back carbon and the dot represents the front carbon. The back carbon is substituted by one hydroxyl, one hydrogen atom and one hydroxymethyl group and the front carbon is substituted by one hydrogen atom, one hydroxyl group and one formyl group. The skeletal structure for the given projection is,

Figure 2

In the given compound, $\text{OH}$, $\text{H}$, $\text{CHO}$ and $\text{C}\left(\text{II}\right)$ groups are attached to $\text{C}\left(\text{I}\right)$. The highest priority group is $\text{OH}$ because the atomic number is higher. The carbon atom of group $\text{CHO}$ is bonded to oxygen atom whereas carbon atom of $\text{C(II)}$ is bonded to three different groups. The prioritization of groups is shown in Figure 2. Hence, the $R$ or $S$ configuration around two stereogenic centers are, $\text{C}\left(\text{I}\right)$ $R$, $\text{C}\left(\text{II}\right)$ $R$.

The given Newman projection D is,

Figure 7

In Newman projection the circle represents the back carbon and the dot represents the front carbon. The back carbon is substituted by one hydroxyl, one hydrogen atom and one hydroxymethyl group and the front carbon is substituted by one hydrogen atom, one hydroxyl group and one formyl group. The skeletal structure for the given projection is,

Figure 8

In the given compound, $\text{OH}$, $\text{H}$, $\text{CHO}$ and $\text{C}\left(\text{II}\right)$ groups are attached to $\text{C}\left(\text{I}\right)$. The highest priority group is $\text{OH}$ because the atomic number is higher. The carbon atom of group $\text{CHO}$ is bonded to oxygen atom whereas carbon atom of $\text{C(II)}$ is bonded to three different groups. The prioritization of groups is shown in Figure 8. Hence, the $R$ or $S$ configuration around two stereogenic centers are, $\text{C}\left(\text{I}\right)$ $S$, $\text{C}\left(\text{II}\right)$ $R$.

Both A and D have one stereogenic centre with same configuration and one with opposite configuration. Hence, A and D are diastereomers.

Conclusion

Compounds A and D are diastereomers.

Interpretation Introduction

(d)

Interpretation: The relation between the compounds C and D is to be determined.

Concept introduction: Newman projections are drawn to visualize the different conformations of a compound around $\text{C}-\text{C}$ bond. In Newman projection the circle represents the back carbon and the dot represents the front carbon.

Enantiomer of a compound has opposite configuration at stereogenic centers. Diastereomers of a compound have at least one stereogenic centre with same configuration and at least one with opposite configuration.

Answer to Problem 5.61P

Compounds C and D are diastereomers.

Explanation of Solution

The given Newman projection C is,

Figure 5

In Newman projection the circle represents the back carbon and the dot represents the front carbon. The back carbon is substituted by one hydroxyl, one hydrogen atom and one hydroxymethyl group and the front carbon is substituted by one hydrogen atom, one hydroxyl group and one formyl group. The skeletal structure for the given projection is,

Figure 6

In the given compound, $\text{OH}$, $\text{H}$, $\text{CHO}$ and $\text{C}\left(\text{II}\right)$ groups are attached to $\text{C}\left(\text{I}\right)$. The highest priority group is $\text{OH}$ because the atomic number is higher. The carbon atom of group $\text{CHO}$ is bonded to oxygen atom whereas carbon atom of $\text{C(II)}$ is bonded to three different groups. The prioritization of groups is shown in Figure 6. Hence, the $R$ or $S$ configuration around two stereogenic centers are, $\text{C}\left(\text{I}\right)$ $S$, $\text{C}\left(\text{II}\right)$ $S$.

The given Newman projection D is,

Figure 7

In Newman projection the circle represents the back carbon and the dot represents the front carbon. The back carbon is substituted by one hydroxyl, one hydrogen atom and one hydroxymethyl group and the front carbon is substituted by one hydrogen atom, one hydroxyl group and one formyl group. The skeletal structure for the given projection is,

Figure 8

In the given compound, $\text{OH}$, $\text{H}$, $\text{CHO}$ and $\text{C}\left(\text{II}\right)$ groups are attached to $\text{C}\left(\text{I}\right)$. The highest priority group is $\text{OH}$ because the atomic number is higher. The carbon atom of group $\text{CHO}$ is bonded to oxygen atom whereas carbon atom of $\text{C(II)}$ is bonded to three different groups. The prioritization of groups is shown in Figure 8. Hence, the $R$ or $S$ configuration around two stereogenic centers are, $\text{C}\left(\text{I}\right)$ $S$, $\text{C}\left(\text{II}\right)$ $R$.

Both C and D have one stereogenic centre with same configuration and one with opposite configuration. Hence, compounds C and D are diastereomers.

Conclusion

Compounds C and D are diastereomers.