NEET Chemistry: Benzene structure and aromaticity Practice Questions

Correct answer: A — The stabilization provided by resonance and electron delocalization

The small energy difference is the manifestation of resonance stabilization, where the actual structure is a resonance hybrid of all possible Kekulé forms.

Correct answer: D — Resonance energy

Aromatic stability is derived from the extensive delocalization of π electrons, which leads to resonance stabilization energy, making the aromatic system significantly more stable than a hypothetical localized structure.

Correct answer: D — A stable, cyclic, and highly stable structure with equal bond lengths.

The delocalization of pi electrons across the cyclic structure of benzene leads to a highly stable configuration. This extensive delocalization results in a planar geometry and highly symmetrical bond lengths, which contributes significantly to its aromatic stability.

Correct answer: B — Six π electrons are delocalized, resulting in a stable cyclic system.

Benzene possesses six π electrons (one from each C-H bond) that are delocalized over the entire cyclic structure, making it an aromatic system. This cyclic delocalization leads to significant stabilization (aromaticity).

Correct answer: B — The system must have an odd number of π electrons.

Aromaticity requires an even number of π electrons of the (4n+2) rule, not an odd number. The other three options describe the essential geometrical and electron system requirements.

Correct answer: B — n=1

For benzene, the number of π electrons is 6. Setting 4n+2 = 6, we get 4n = 4, so n=1. This confirms that benzene obeys Hückel's rule with n=1.

Correct answer: D — The extended π-electron delocalization.

The significant stability of benzene arises from the complete delocalization of the six π-electrons across the ring, leading to a lower overall energy state compared to non-aromatic cyclic alkenes.

Correct answer: B — 4n + 2 π electrons

Hückel's rule states that a planar, cyclic, fully conjugated system is aromatic if it has (4n + 2) π electrons, where n is an integer (0, 1, 2...). For benzene, n=1, so 4(1)+2=6 electrons.

Correct answer: D — Benzene

Benzene is a planar, hexagonal ring structure, which is a necessary condition for the effective overlap of p-orbitals and the delocalization of π electrons, thus confirming its aromaticity.

Correct answer: D — Cyclohexa-1,3,5-triene

Cyclohexa-1,3,5-triene has 6 π-electrons, which satisfies Hückel's rule (4n+2, where n=1). Cyclohexene and cycloheptatriene are not fully aromatic.

Correct answer: D — 6

Benzene is a cyclic molecule with 6 carbon atoms. Each carbon atom contributes one p-orbital, leading to 6 delocalized π electrons. This conforms to Hückel's rule for aromaticity (4n+2, where n=1).

Correct answer: D — delocalized π electron system.

Benzene exhibits a delocalized system of π electrons spread across the entire ring, which is the basis of its aromaticity.

Correct answer: D — The molecule features a continuous, delocalized π electron system across the cyclic structure.

Benzene is characterized by a cyclic, planar structure where the six carbon atoms are connected by delocalized π electrons forming a continuous, highly stable aromatic system. This delocalization is the source of its aromaticity.

Correct answer: A — 6

Benzene is a six-membered ring, and each carbon atom contributes one p-orbital, resulting in 6 × 2 = 12 π electrons, or 6 π electrons if considering the delocalized system count (4 in the ring structure, 2 localized). For Hückel's rule, we count the system as a whole, which is 6 π electrons within the cyclic system.