Chapter C, Problem C.10P

Interpretation Introduction

(a)

Interpretation:

The R or S configuration of the chiral center in the given molecule is to be designated.

Concept introduction:

When assigning priorities to substituents, the atom having the greater atomic number has the higher priority. In case of comparison between isotopes, the one having the greater atomic mass gets the higher priority. Substituents with double/triple bonds are treated differently from the substituents having only single bonds. An atom that is doubly bonded to another atom is treated as having two single bonds to the atom – one real (shown in black) and one imaginary (shown in red). An atom that is triply bonded to another atom is treated as having three single bonds to the atom – one real (shown in black) and two imaginary (shown in red).

When the fourth priority substituent is pointing away (it is attached by a dash bond) and the first, second, and third priority substituents are arranged clockwise, the configuration is R.

When the fourth priority substituent is pointing away (it is attached by a dash bond) and the first, second, and third priority substituents are arranged counterclockwise, the configuration is S.

If the fourth priority substituent is attached by a wedge bond, then the clockwise or counterclockwise arrangement of the first, second, and third priority substituents is determined, and that arrangement is reversed before assigning R or S.

Answer to Problem C.10P

The configuration of the chiral carbon atom in the given molecule is designated as S.

Explanation of Solution

The given molecule is

The IUPAC name for the above molecule, without considering the stereochemistry, would be $\text{4-bromo-2-methyl-2-hexene}$.

There is one chiral center in this molecule, and the substituents attached to it are ${\text{Br, CH}}_2{\text{CH}}_3\text{ , CH=C and H}$. Applying the first tiebreaker, the $\text{Br}$ atom gets the first priority, and $\text{H}$ atom gets the fourth priority.

In the structure, the $C=C$ double bond has been replaced by a single bond, and single bonds to two imaginary C atoms (red) have been added as shown below:

The second and third position priorities are decided by the set of atoms one bond away from the respective points of attachment. The set for the ethyl substituent, which is located on the right, is $\{C,H,H\}$, and the set of atoms for the substituent on left is $\{C,C,H\}$. Comparing the highest-priority substituents from each set, the substituent on the left wins and gets the second priority. Given that these substituents are arranged counterclockwise with the fourth-priority substituent away, the configuration at the chiral center is assigned as S. Thus, the configuration at the chiral center for the molecule $\text{4-bromo-2-methyl-2-hexene}$ is S.

Conclusion

The configuration at the chiral center of the molecule is designated as above.

Interpretation Introduction

(b)

Interpretation:

The R or S configuration of the chiral center in the given molecule is to be designated.

Concept introduction:

When assigning priorities to substituents, the atom having the greater atomic number has the higher priority. In case of comparison between isotopes, the one having the greater atomic mass gets the higher priority. Substituents with double/triple bonds are treated differently from the substituents having only single bonds. An atom that is doubly bonded to another atom is treated as having two single bonds to the atom – one real (shown in black) and one imaginary (shown in red). An atom that is triply bonded to another atom is treated as having three single bonds to the atom – one real (shown in black) and two imaginary (shown in red).

When the fourth priority substituent is pointing away (it is attached by a dash bond) and the first, second, and third priority substituents are arranged clockwise, the configuration is R.

When the fourth priority substituent is pointing away (it is attached by a dash bond) and the first, second, and third priority substituents are arranged counterclockwise, the configuration is S.

If the fourth priority substituent is attached by a wedge bond, then the clockwise or counterclockwise arrangement of the first, second, and third priority substituents is determined, and that arrangement is reversed before assigning R or S.

If the fourth priority substituent is in the plane of the page, then it is switched with the substituent that points away. Then the clockwise or counterclockwise arrangement of the first, second, and third priority substituents is determined, and that arrangement is reversed before assigning R or S.

Answer to Problem C.10P

The configuration of the chiral carbon atom in the given molecule is designated as R.

Explanation of Solution

The given molecule is

The IUPAC name for the above molecule, without considering the stereochemistry, would be $3,4,4-trimethylpent-5-ene$.

There is one chiral center in this molecule, and the substituents attached to it are ${\text{CH}}_3{\text{ , CH=CH}}_2{\text{ , C(CH}}_3{\text{)}}_2\text{ and H}$. Applying the first tiebreaker, the $\text{H}$ atom gets the fourth priority. All the remaining substituents are attached by the carbon atom to the chiral center. In the structure, the $C=C$ double bond has been replaced by a single bond, and single bonds to two imaginary C atoms (red) have been added as shown below:

The first three top-priority substituents are decided by the set of atoms one bond away from the respective points of attachment. The set for the substituent, which is located on the right, is $\{C,C,C\}$; the set of atoms for the substituent on the left is $\{C,C,H\}$, and the set of atoms for the methyl substituent is $\{H,H,H\}$. Comparing the highest-priority substituents from each set, the substituent on the right wins and gets the first priority while the substituent on the left gets the second priority. Methyl substituent gets the third priority. Given that these substituents are arranged counterclockwise but since the fourth-priority substituent is attached by a wedge bond, the arrangement is reversed, and so the configuration at the chiral center is R. Thus, the configuration at the chiral center for the molecule $3,4,4-trimethylpent-5-ene$ is R.

Conclusion

The configuration at the chiral center of the molecule is designated as above.

Interpretation Introduction

(c)

Interpretation:

The R or S configuration of the chiral center in the given molecule is to be designated.

Concept introduction:

When assigning priorities to substituents, the atom having the greater atomic number has the higher priority. In case of comparison between isotopes, the one having the greater atomic mass gets the higher priority. Substituents with double/triple bonds are treated differently from the substituents having only single bonds. An atom that is doubly bonded to another atom is treated as having two single bonds to the atom – one real (shown in black) and one imaginary (shown in red). An atom that is triply bonded to another atom is treated as having three single bonds to the atom – one real (shown in black) and two imaginary (shown in red).

When the fourth priority substituent is pointing away (it is attached by a dash bond) and the first, second, and third priority substituents are arranged clockwise, the configuration is R.

When the fourth priority substituent is pointing away (it is attached by a dash bond) and the first, second, and third priority substituents are arranged counterclockwise, the configuration is S.

If the fourth priority substituent is attached by a wedge bond, then the clockwise or counterclockwise arrangement of the first, second, and third priority substituents is determined, and that arrangement is reversed before assigning R or S.

If the fourth priority substituent is in the plane of the page, then it is switched with the substituent that points away. Then the clockwise or counterclockwise arrangement of the first, second, and third priority substituents is determined, and that arrangement is reversed before assigning R or S.

Answer to Problem C.10P

The configuration of the chiral carbon atom in the given molecule is designated as R.

Explanation of Solution

The given molecule is

The IUPAC name for the above molecule, without considering the stereochemistry, would be $\text{6-methyl-4-nitrohept-5-en-1-yne}$. The molecule contains one double bond and one triple bond. There is one chiral center in this molecule, and the substituents attached to it are ${\text{NO}}_2{\text{, CH}}_2\text{C}\equiv {\text{C, CH=C(CH}}_3{\text{)}}_2\text{ and H}$. Applying the first tiebreaker, the $\text{H}$ atom gets the fourth priority while $\text{N}$ atom gets the first priority. The remaining two substituents are attached by the carbon atom to the chiral center. In the structure, the $C=C$ double bonds and $C\equiv C$ triple bonds have been replaced by a single bond to two and four imaginary C atoms (red) as shown below:

The second and third priority substituents are decided by the set of atoms one bond away from the respective points of attachment. The set for the substituent, which is located on the right, is $\{C,H,H\}$; the set of atoms for the substituent on the left containing the double bond is $\{C,C,H\}$. Comparing the highest-priority substituents from each set, the substituent on the left wins and gets the second priority while the substituent on the right gets the third priority. Given that these substituents are arranged in the clockwise manner and the fourth-priority substituent is attached by a dash bond, the arrangement is considered clockwise, and the configuration at the chiral center is R. Thus, the configuration at the chiral center for the molecule $\text{6-methyl-4-nitrohept-5-en-1-yne}$ is R.

Conclusion

The configuration at the chiral center of the molecule is designated as above.

Interpretation Introduction

(d)

Interpretation:

The R or S configuration of the chiral center in the given molecule is to be designated.

Concept introduction:

When assigning priorities to substituents, the atom having the greater atomic number has the higher priority. In case of comparison between isotopes, the one having the greater atomic mass gets the higher priority. Substituents with double/triple bonds are treated differently from the substituents having only single bonds. An atom that is doubly bonded to another atom is treated as having two single bonds to the atom – one real (shown in black) and one imaginary (shown in red). An atom that is triply bonded to another atom is treated as having three single bonds to the atom – one real (shown in black) and two imaginary (shown in red).

When the fourth priority substituent is pointing away (it is attached by a dash bond) and the first, second, and third priority substituents are arranged clockwise, the configuration is R.

When the fourth priority substituent is pointing away (it is attached by a dash bond) and the first, second, and third priority substituents are arranged counterclockwise, the configuration is S.

If the fourth priority substituent is attached by a wedge bond, then the clockwise or counterclockwise arrangement of the first, second, and third priority substituents is determined, and that arrangement is reversed before assigning R or S.

If the fourth priority substituent is in the plane of the page, then it is switched with the substituent that points away. Then the clockwise or counterclockwise arrangement of the first, second, and third priority substituents is determined, and that arrangement is reversed before assigning R or S.

Answer to Problem C.10P

The configuration of the chiral carbon atom in the given molecule is designated as R.

Explanation of Solution

The given molecule is

The molecule contains two triple bonds. There is one chiral center in this molecule, and the substituents attached to it are ${\text{CH}}_3\text{, C}\equiv \text{N, C}\equiv \text{CH, and H}$. Applying the first tiebreaker, the $\text{H}$ atom gets the fourth priority. The remaining three substituents are attached by the carbon atom to the chiral center. In the structure, each $C\equiv C$ triple bond has been replaced by two imaginary C atoms (red) as shown below:

The top three-priorities are decided by the set of atoms one bond away from the respective points of attachment.

The set for the substituent, which is located on the right, is $\{N,C,C\}$; the set of atoms for the substituent on bottom-left containing the triple bond is $\{C,C,C\}$, and the set of atoms for the methyl substituent is $\{H,H,H\}$. Thus, the methyl substituent gets the third priority. The substituent on the right gets the first priority while the substituent on the bottom-left gets the second priority.

Given that these substituents are arranged in the counterclockwise manner, but since the fourth-priority substituent is attached by a wedge bond, the arrangement is considered as reverse, that is, clockwise, and the configuration at the chiral center is R. Thus, the configuration at the chiral center for the molecule is R.

Conclusion

The configuration at the chiral center of the molecule is designated as above.

Interpretation Introduction

(e)

Interpretation:

The R or S configuration of the chiral center in the given molecule is to be designated.

Concept introduction:

When assigning priorities to substituents, the atom having the greater atomic number has the higher priority. In case of comparison between isotopes, the one having the greater atomic mass gets the higher priority. Substituents with double/triple bonds are treated differently from the substituents having only single bonds. An atom that is doubly bonded to another atom is treated as having two single bonds to the atom – one real (shown in black) and one imaginary (shown in red). An atom that is triply bonded to another atom is treated as having three single bonds to the atom – one real (shown in black) and two imaginary (shown in red).

When the fourth priority substituent is pointing away (it is attached by a dash bond) and the first, second, and third priority substituents are arranged clockwise, the configuration is R.

When the fourth priority substituent is pointing away (it is attached by a dash bond) and the first, second, and third priority substituents are arranged counterclockwise, the configuration is S.

If the fourth priority substituent is attached by a wedge bond, then the clockwise or counterclockwise arrangement of the first, second, and third priority substituents is determined, and that arrangement is reversed before assigning R or S.

If the fourth priority substituent is in the plane of the page, then it is switched with the substituent that points away. Then the clockwise or counterclockwise arrangement of the first, second, and third priority substituents is determined, and that arrangement is reversed before assigning R or S.

Answer to Problem C.10P

The configuration of the chiral carbon atom in the given molecule is designated as R.

Explanation of Solution

The given molecule is

The molecule contains one double bond and one triple bond. There is one chiral center in this molecule, and the substituents attached to it are ${\text{NO}}_2{\text{, CH}}_2{\text{CH}}_2\text{C}\equiv {\text{C, CH=C(CH}}_3{\text{)}}_2\text{ and H}$. Applying the first tiebreaker, the $\text{H}$ atom gets the fourth priority while the $\text{N}$ atom gets the first priority. The remaining two substituents are attached by the carbon atom to the chiral center. In the structure, the $C=C$ double bond and $C\equiv C$ triple bond are replaced by a single bond by four imaginary C atoms (red) as shown below:

The second and third priority substituents are decided by the set of atoms one bond away from the respective points of attachment. The set for the substituent, which is located on the right, is $\{C,H,H\}$; the set of atoms for the substituent on the left containing the double bond is $\{C,C,H\}$. Comparing the highest-priority substituents from each set, the substituent on the left wins and gets the second priority while the substituent on the right gets the third priority. Given that these substituents are arranged in the clockwise manner and the fourth-priority substituent is attached by a dash bond, the arrangement is considered clockwise, and the configuration at the chiral center is R. Thus, the configuration at the chiral center for the molecule $\text{6-methyl-4-nitrohept-5-en-1-yne}$ is R.

Conclusion

The configuration at the chiral center of the molecule is designated as above.