Chapter 14, Problem 14.11P

Interpretation Introduction

(a)

Interpretation:

The given molecule is to be identified as aromatic, antiaromatic, or nonaromatic.

Concept introduction:

Huckel’s rule for aromaticity states that if a species is planar and possesses a $\text{π}$-system of molecular orbitals constructed from p-orbitals that are fully conjugated around a ring (${\text{sp}}^2$ hybridized), then the species is aromatic if the number of electrons in that $\text{π}$- system fits the formula $\text{4n+2 (n = 0, 1, 2, }\mathrm{...}\text{)}$. It is antiaromatic if the number of electrons in that $\text{π}$- system fits the formula $\text{4n (n = 0, 1, 2, }\mathrm{...}\text{)}$. All other species are considered nonaromatic.

Answer to Problem 14.11P

The given molecule is nonaromatic.

Explanation of Solution

The structure of the given molecule is

In the given compound, six carbon atoms are ${\text{sp}}^{\text{2}}$ hybridized, and the remaining four carbons are ${\text{sp}}^{\text{3}}$ hybridized.

Because of the ${\text{sp}}^{\text{3}}$ hybridized C5, C6, C9, and C10, the molecule will not be planar. These atoms also interrupt the conjugation.

Therefore, this molecule is nonaromatic.

Conclusion

The presence of four ${\text{sp}}^{\text{3}}$ hybridized carbon atoms in ring indicates that the molecule is nonaromatic.

Interpretation Introduction

(b)

Interpretation:

The given molecule is to be identified as aromatic, antiaromatic, or nonaromatic.

Concept introduction:

Huckel’s rule for aromaticity states that if a species is planar and possesses a $\text{π}$-system of molecular orbitals constructed from p-orbitals that are fully conjugated around a ring (${\text{sp}}^2$ hybridized), then the species is aromatic if the number of electrons in that $\text{π}$- system fits the formula $\text{4n+2 (n = 0, 1, 2, }\mathrm{...}\text{)}$. These numbers are called Huckel numbers. It is antiaromatic if the number of electrons in that $\text{π}$- system fits the formula $\text{4n (n = 0, 1, 2, }\mathrm{...}\text{)}$. All other species are considered nonaromatic.

Answer to Problem 14.11P

The given molecule is aromatic.

Explanation of Solution

Structure of the given molecule is

In this molecule, six carbon atoms are ${\text{sp}}^{\text{2}}$ hybridized, and the remaining four carbons are ${\text{sp}}^{\text{3}}$ hybridized. The six $\text{π}$-electrons in the ring on the left are completely conjugated, making it aromatic. The four ${\text{sp}}^{\text{3}}$ hybridized carbons are not a part of this ring.

Therefore, the given molecule is aromatic.

Conclusion

The presence of six $\text{π}$ electrons (a Huckel number) in completely conjugated cyclic $\text{π}$-system indicates that the molecule is aromatic.

Interpretation Introduction

(c)

Interpretation:

The given molecule is to be identified as aromatic, antiaromatic, or nonaromatic.

Concept introduction:

Huckel’s rule for aromaticity states that if a species is planar and possesses a $\text{π}$-system of molecular orbitals constructed from p-orbitals that are fully conjugated around a ring (${\text{sp}}^2$ hybridized), then the species is aromatic if the number of electrons in that $\text{π}$- system fits the formula $\text{4n+2 (n = 0, 1, 2, }\mathrm{...}\text{)}$. It is antiaromatic if the number of electrons in that $\text{π}$- system fits the formula $\text{4n (n = 0, 1, 2, }\mathrm{...}\text{)}$. All other species are considered nonaromatic.

Answer to Problem 14.11P

The given molecule is nonaromatic.

Explanation of Solution

Structure of the given molecule is

In the given compound, four carbon atoms are ${\text{sp}}^{\text{2}}$ hybridized, and the remaining carbon, C4, is ${\text{sp}}^{\text{3}}$ hybridized. There are four electrons in the $\text{π}$-system, but it is not completely cyclic because of the presence of the ${\text{sp}}^{\text{3}}$ carbon.

Therefore, the given molecule is nonaromatic.

Conclusion

The presence of one ${\text{sp}}^{\text{3}}$ hybridized carbon atom in the ring indicates that the molecule is nonaromatic.

Interpretation Introduction

(d)

Interpretation:

The given molecule is to be identified as aromatic, antiaromatic, or nonaromatic.

Concept introduction:

Huckel’s rule for aromaticity states that if a species is planar and possesses a $\text{π}$-system of molecular orbitals constructed from p-orbitals that are fully conjugated around a ring (${\text{sp}}^2$ hybridized), then the species is aromatic if the number of electrons in that $\text{π}$- system fits the formula $\text{4n+2 (n = 0, 1, 2, }\mathrm{...}\text{)}$. It is antiaromatic if the number of electrons in that $\text{π}$- system fits the formula $\text{4n (n = 0, 1, 2, }\mathrm{...}\text{)}$. All other species are considered nonaromatic.

Answer to Problem 14.11P

The given molecule is nonaromatic.

Explanation of Solution

Structure of the given molecule is

In the given compound, six carbon atoms are ${\text{sp}}^{\text{2}}$ hybridized, and the remaining one, C6, is ${\text{sp}}^{\text{3}}$ hybridized. The $\text{π}$-system is not completely cyclic because of the presence of the ${\text{sp}}^{\text{3}}$ carbon.

Therefore, the given molecule is nonaromatic.

Conclusion

The presence of one ${\text{sp}}^{\text{3}}$ hybridized carbon atom in ring indicates that the molecule is nonaromatic.

Interpretation Introduction

(e)

Interpretation:

The given molecule is to be identified as aromatic, antiaromatic, or nonaromatic.

Concept introduction:

Huckel’s rule for aromaticity states that if a species is planar and possesses a $\text{π}$-system of molecular orbitals constructed from p-orbitals that are fully conjugated around a ring (${\text{sp}}^2$ hybridized), then the species is aromatic if the number of electrons in that $\text{π}$- system fits the formula $\text{4n+2 (n = 0, 1, 2, }\mathrm{...}\text{)}$. It is antiaromatic if the number of electrons in that $\text{π}$- system fits the formula $\text{4n (n = 0, 1, 2, }\mathrm{...}\text{)}$. All other species are considered nonaromatic.

Answer to Problem 14.11P

The given molecule is nonaromatic.

Explanation of Solution

Structure of the given molecule is

In the given compound, two carbon atoms are ${\text{sp}}^{\text{2}}$ hybridized, and the remaining two, C3 and C4, are ${\text{sp}}^{\text{3}}$ hybridized. The $\text{π}$ system is not completely cyclic because of the presence of the two ${\text{sp}}^{\text{3}}$ hybridized carbon atoms.

Therefore, the given molecule is nonaromatic.

Conclusion

The presence of two ${\text{sp}}^{\text{3}}$ hybridized carbon atoms in the ring indicates that the molecule is nonaromatic.

Interpretation Introduction

(f)

Interpretation:

The given molecule is to be identified as aromatic, antiaromatic, or nonaromatic.

Concept introduction:

Huckel’s rule for aromaticity states that if a species is planar and possesses a $\text{π}$-system of molecular orbitals constructed from p-orbitals that are fully conjugated around a ring (${\text{sp}}^2$ hybridized), then the species is aromatic if the number of electrons in that $\text{π}$- system fits the formula $\text{4n+2 (n = 0, 1, 2, }\mathrm{...}\text{)}$. It is antiaromatic if the number of electrons in that $\text{π}$- system fits the formula $\text{4n (n = 0, 1, 2, }\mathrm{...}\text{)}$. All other species are considered nonaromatic.

Answer to Problem 14.11P

The given molecule is nonaromatic.

Explanation of Solution

Structure of the given molecule is

The molecule is not a cyclic system.

Therefore, the given molecule is nonaromatic.

Conclusion

Non-cyclic form of the given molecule indicates that the molecule is nonaromatic.

Interpretation Introduction

(g)

Interpretation:

The given molecule is to be identified as aromatic, antiaromatic, or nonaromatic.

Concept introduction:

Huckel’s rule for aromaticity states that if a species is planar and possesses a $\text{π}$-system of molecular orbitals constructed from p-orbitals that are fully conjugated around a ring (${\text{sp}}^2$ hybridized), then the species is aromatic if the number of electrons in that $\text{π}$- system fits the formula $\text{4n+2 (n = 0, 1, 2, }\mathrm{...}\text{)}$. It is antiaromatic if the number of electrons in that $\text{π}$ system fits the formula $\text{4n (n = 0, 1, 2, }\mathrm{...}\text{)}$. All other species are considered nonaromatic.

Answer to Problem 14.11P

The given molecule is aromatic.

Explanation of Solution

The structure of the given molecule is

The molecule has a cyclic part with alternating single and double bonds. This means all ring atoms are ${\text{sp}}^2$ hybridized. The ring has a completely cyclic, conjugated $\text{π}$ system containing six electrons, a Huckel number.

Therefore, this molecule is aromatic.

Conclusion

The presence of six $\text{π}$ electrons (a Huckel number) in a completely conjugated cyclic $\text{π}$-system indicates that the molecule is aromatic.