Quiz - Benzene and Aromaticity - 1 | Benzene and Aromaticity

Organic Chemistry 2 - Quiz - Benzene and Aromaticity - 1


The delocalized π system in benzene is formed by a cyclic overlap of:

In benzene, each carbon atom is sp2 hybridized, which means it has three hybrid orbitals: one σ bond formed by overlapping with a hydrogen atom, and two π bonds formed by the overlap of p orbitals. The p orbitals that are not involved in σ bonding form a delocalized π system above and below the plane of the carbon atoms.


Which of the following statements is correct about benzene?

Benzene is a planar hexagonal molecule where all six carbon atoms lie in the same plane, and the carbon-carbon (C-C) bond lengths are equal. The unique feature of benzene is its delocalized π system, formed by the cyclic overlap of six p orbitals, resulting in a continuous ring of electron density above and below the carbon atom plane. This delocalization of electrons contributes to the stability and aromaticity of benzene, making it a special class of compounds.


Which molecule would be considered nonaromatic according to Hückel's rule?

Hückel's rule states that for a compound to be aromatic, it must have (4n + 2) π electrons, where n is a non-negative integer. Cyclobutadiene has 4 π electrons, failing the (4n + 2) rule, and is thus considered nonaromatic.


What criterion must a compound meet to be considered aromatic?

According to Hückel's rule, aromatic compounds must have a planar, cyclic structure and a continuous loop of 4n+2 π electrons to exhibit aromaticity


What contributes to the exceptional stability of aromatic compounds such as benzene?

Aromatic stability results from the delocalization of π electrons throughout the ring, resulting in a more stable, planar structure. This delocalization results in a lower energy state, making aromatic compounds energetically favorable.


Cyclohepta-1,3,5-triene is:

Cyclohepta-1,3,5-triene is nonaromatic because it does not satisfy the criteria for aromaticity. Although it is cyclic and planar, it lacks continuous conjugation of π electrons. The alternating single and double bonds create a non-conjugated system, and as a result, the molecule does not exhibit the enhanced stability associated with aromatic compounds.


Which compound is an example of an aromatic heterocycle?


Pyridine is an aromatic heterocycle because it exhibits planarity, continuous conjugation,  has 6 π electrons in its six-membered ring (satisfying Hückel's Rule), and contains a nitrogen heteroatom. The presence of nitrogen enhances, rather than disrupts, the overall stability of its aromatic system.


Which of the following is an example of a PAH?

Naphthalene is a polycyclic aromatic hydrocarbon (PAH): it consists of 2 fused aromatic rings forming a planar structure with π electrons delocalized across the entire fused ring system.


Which of the following is an example of a reagent used for catalytic hydrogenation of aromatic compounds?

Hydrogenation of aromatic compounds requires a catalyst (often nickel), elevated temperatures (around 150-300°C) and high pressures (typically several atmospheres) to overcome the stability of the benzene ring.


What is the product of the Birch reduction of benzene?

The Birch reduction of benzene typically produces 1,4-cyclohexadiene as the major product. This reaction involves the addition of two electrons and two protons to the benzene ring.