Chapter 1, Problem 1.82P

Stalevo is the trade name for a medication used fssor Parkinson’s disease, which contains L-dopa, carbidopa, and entacapone.

a. Draw a Lewis structure for entacapone.

b. Which $\text{C}-\text{C}$ bond in entacapone is the longest?

c. Which $\text{C}-\text{C}$ single bond is the shortest?

d. Which $\text{C}-\text{N}$ bond is the longest?

e. Which $\text{C}-\text{N}$ bond is the shortest?

f. Use curved arrows to draw a resonance structure that is an equal contributor to the resonance hybrid.

g. Use curved arrows to draw a resonance structure that is a minor contributor to the resonance hybrid.

Interpretation Introduction

(a)

Interpretation: A Lewis structure for entacapone is to be drawn.

Concept introduction: One should follow the given steps to draw the Lewis structure of a given skeleton structure. The first step is placing a $\text{C}$ atom at the intersection and at the end of any two lines. The second step is addition of enough hydrogen to make each carbon atom tetravalent. The third step is providing the lone pairs to heteroatom to complete an octet.

Answer to Problem 1.82P

A Lewis structure for entacapone is,

Explanation of Solution

The given structure of entacapone is in skeleton form.

One should follow the given steps to draw the Lewis structure of a given skeleton structure. The first step is placing a $\text{C}$ atom at the intersection and at the end of any two lines. The second step is addition of enough hydrogen to make each carbon atom tetravalent. The third step is providing the lone pairs to heteroatom to complete an octet.

Thus, a Lewis structure for entacapone is,

Figure 1

Conclusion

A Lewis structure for entacapone is shown in Figure 1.

Interpretation Introduction

(b)

Interpretation: The longest $\text{C}-\text{C}$ bond in entacapone is to be identified.

Concept introduction: Bond length is inversely proportional to the number of electrons present between two nuclei. This means as the number of electrons present between two nuclei increases bond length becomes shorter and stronger.

Answer to Problem 1.82P

The $-{\text{CH}}_{\text{2}}\text{CH}{\text{3}}_{}$ group contains longest $\text{C}-\text{C}$ bond in entacapone (labeled by red color).

Explanation of Solution

Bond length is inversely proportional to the number of electrons present between two nuclei. This means as the number of electrons present between two nuclei increases bond length becomes shorter and stronger.

Therefore, triple bonds are stronger and shorter than double bonds, which are stronger than single bonds.

The longest $\text{C}-\text{C}$ bond in entacapone is labeled by red color as shown below.

Figure 2

Thus, the $-{\text{CH}}_{\text{2}}\text{CH}{\text{3}}_{}$ group contains longest $\text{C}-\text{C}$ bond in entacapone.

Conclusion

The $-{\text{CH}}_{\text{2}}\text{CH}{\text{3}}_{}$ group contains longest $\text{C}-\text{C}$ bond in entacapone.

Interpretation Introduction

(c)

Interpretation: The shortest $\text{C}-\text{C}$ single bond in entacapone is to be identified.

Concept introduction: Bond length is inversely proportional to the number of electrons present between two nuclei. This means as the number of electrons present between two nuclei increases bond length becomes shorter and stronger.

Answer to Problem 1.82P

The shortest $\text{C}-\text{C}$ single bond is attached to $-\text{C}\equiv \text{N}$ in entacapone (labeled by red color).

Explanation of Solution

Bond length is inversely proportional to the number of electrons present between two nuclei. This means as the number of electrons present between two nuclei increases bond length becomes shorter and stronger.

Therefore, triple bonds are stronger and shorter than double bonds, which are stronger than single bonds.

The shortest $\text{C}-\text{C}$ single bond in entacapone is labeled by red color as shown below.

Figure 3

Thus, the shortest $\text{C}-\text{C}$ single bond is attached to $-\text{C}\equiv \text{N}$ in entacapone.

Conclusion

The shortest $\text{C}-\text{C}$ single bond is attached to $-\text{C}\equiv \text{N}$ in entacapone.

Interpretation Introduction

(d)

Interpretation: The longest $\text{C}-\text{N}$ bond in entacapone is to be identified.

Concept introduction: Bond length is inversely proportional to the number of electrons present between two nuclei. This means as the number of electrons present between two nuclei increases bond length becomes shorter and stronger.

Answer to Problem 1.82P

The longest $\text{C}-\text{N}$ bond in entacapone is attached to $-{\text{CH}}_2{\text{CH}}_{\text{3}}$ group (labeled by red color).

Explanation of Solution

Bond length is inversely proportional to the number of electrons present between two nuclei. This means as the number of electrons present between two nuclei increases bond length becomes shorter and stronger.

Therefore, triple bonds are stronger and shorter than double bonds, which are stronger than single bonds.

The longest $\text{C}-\text{N}$ bond in entacapone is labeled by red color as shown below.

Figure 4

Thus, the longest $\text{C}-\text{N}$ bond in entacapone is attached to $-{\text{CH}}_2{\text{CH}}_{\text{3}}$ group.

Conclusion

The longest $\text{C}-\text{N}$ bond in entacapone is attached to $-{\text{CH}}_2{\text{CH}}_{\text{3}}$ group.

Interpretation Introduction

(e)

Interpretation: The shortest $\text{C}-\text{N}$ bond in entacapone is to be identified.

Concept introduction: Bond length is inversely proportional to the number of electrons present between two nuclei. This means as the number of electrons present between two nuclei increases bond length becomes shorter and stronger.

Answer to Problem 1.82P

The shortest $\text{C}-\text{N}$ bond in entacapone is $-\text{C}\equiv \text{N}$ bond (labeled by red color).

Explanation of Solution

Bond length is inversely proportional to the number of electrons present between two nuclei. This means as the number of electrons present between two nuclei increases bond length becomes shorter and stronger.

Therefore, triple bonds are stronger and shorter than double bonds, which are stronger than single bonds.

The shortest $\text{C}-\text{N}$ bond in entacapone is labeled by red color as shown below.

Figure 5

Thus, the shortest $\text{C}-\text{N}$ bond in entacapone is $-\text{C}\equiv \text{N}$ bond.

Conclusion

The shortest $\text{C}-\text{N}$ bond in entacapone is $-\text{C}\equiv \text{N}$ bond.

Interpretation Introduction

(f)

Interpretation: A resonance structure that is an equal contributor to the resonance hybrid in entacapone is to be drawn.

Concept introduction: The delocalization of lone pair or free electrons from one atom to another is known as resonance. The stability of compound depends upon the number of resonating structures. More the resonating structures of compound more will its stability.

Answer to Problem 1.82P

A resonance structure that is an equal contributor to the resonance hybrid in entacapone is drawn below.

Explanation of Solution

The delocalization of lone pair or free electrons from one atom to another is known as resonance. The stability of compound depends upon the number of resonating structures. More the resonating structures of compound more will its stability.

A resonance structure that is an equal contributor to the resonance hybrid in entacapone is drawn below.

Figure 6

Conclusion

A resonance structure that is an equal contributor to the resonance hybrid in entacapone is drawn in Figure 6.

Interpretation Introduction

(g)

Interpretation: A resonance structure that is minor contributor to the resonance hybrid in entacapone is to be drawn.

Concept introduction: The delocalization of lone pair or free electrons from one atom to another is known as resonance. The stability of compound depends upon the number of resonating structures. More the resonating structures of compound more will its stability.

Answer to Problem 1.82P

A resonance structure that is minor contributor to the resonance hybrid in entacapone is drawn below.

Explanation of Solution

The delocalization of lone pair or free electrons from one atom to another is known as resonance. The stability of compound depends upon the number of resonating structures. More the resonating structures of compound more will its stability.

A resonance structure that is minor contributor to the resonance hybrid in entacapone is drawn below.

Figure 7

Conclusion

A resonance structure that is minor contributor to the resonance hybrid in entacapone is drawn in Figure 7.