Question 1

Which of the following criteria must a compound meet to be considered aromatic according to Hückel's rule?

Accepted Answer

It must be cyclic, planar, fully conjugated, and have $$4n+2 pi $$electrons.

Question 2

Benzene is more stable than expected for a molecule with three double bonds. This extra stability is best explained by:

Accepted Answer

The delocalization of pi electrons over the entire ring (resonance energy).

Question 3

Which of the following molecules is antiaromatic?

Accepted Answer

Cyclobutadiene

Question 4

What is the resonance energy of benzene, as estimated by comparing its heat of hydrogenation to that of cyclohexene?

Accepted Answer

$$36$$ kcal/mol

Question 5

Which of the following best describes the molecular orbital (MO) model of benzene?

Accepted Answer

Six 2p orbitals combine to form six molecular orbitals, with three bonding and three antibonding MOs.

Question 6

Which of the following statements about the NMR spectrum of benzene is correct?

Accepted Answer

Aryl hydrogens appear in the region $$\delta 6.5 to$$ $$8.5$$ due to the ring current effect.

Question 7

Which of the following is NOT a requirement for a compound to be aromatic?

Accepted Answer

The compound must have only carbon atoms in the ring.

Question 8

Which of the following heterocyclic compounds is aromatic and contains a nitrogen atom whose lone pair is NOT part of the aromatic pi system?

Accepted Answer

Pyridine

Question 9

Which of the following best explains why [10]annulene is not aromatic?

Accepted Answer

It is not planar due to steric hindrance from internal hydrogens.

Question 10

Which of the following ions is aromatic according to Hückel's rule?

Accepted Answer

Cyclopropenyl cation ($$C_3H_3^+)$$

Question 11

Which of the following best describes the difference between aromatic, antiaromatic, and nonaromatic compounds?

Accepted Answer

Aromatic compounds are cyclic, planar, conjugated, and have $$4n+2 pi $$electrons; antiaromatic compounds are cyclic, planar, conjugated, and have $$4n pi $$electrons; nonaromatic compounds lack one or more of these features.

Question 12

Which of the following statements about the resonance structures of benzene is correct?

Accepted Answer

Benzene is a resonance hybrid of two equivalent Kekulé structures, resulting in equal bond lengths.

Question 13

Which of the following is the correct IUPAC name for a benzene ring with a methyl group at position 1 and a bromine at position 4?

Accepted Answer

p-Bromotoluene

Question 14

Which of the following polycyclic aromatic hydrocarbons (PAHs) is composed of three fused benzene rings in a linear arrangement?

Accepted Answer

Anthracene

Question 15

Which of the following best explains why cyclooctatetraene is not antiaromatic?

Accepted Answer

It is not planar and thus cannot have continuous overlap of p orbitals.

Question 16

Which of the following statements about the IR spectrum of benzene is correct?

Accepted Answer

Benzene shows a C=C stretch absorption at $$1600\ 	ext{cm}^{-1}.$$

Question 17

Which of the following best describes the effect of the ring current in benzene on NMR chemical shifts?

Accepted Answer

It causes aromatic hydrogens to absorb at a higher chemical shift (downfield) than vinylic hydrogens.

Question 18

Which of the following is a correct statement about the basicity of pyridine and pyrrole?

Accepted Answer

Pyridine is a stronger base than pyrrole because its lone pair is not part of the aromatic system.

Question 19

Which of the following best describes the difference between the aromaticity of furan and pyrrole?

Accepted Answer

In furan, one lone pair on oxygen is part of the aromatic pi system, while in pyrrole, the lone pair on nitrogen is part of the aromatic pi system.

Aromatic Compounds and Aromaticity: Structure, Nomenclature, and Properties

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