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Chapter 1: Problem 62

In benzene all the \(\mathrm{C}-\mathrm{C}\) bonds are of equal length because of (a) resonance (b) aromaticity (c) hyperconjugation (d) tautomerism

Short Answer

Expert verified
Answer: The reason for all C-C bonds in benzene being of equal length is resonance.

Step by step solution

01

Understanding benzene structure

Benzene (C6H6) is a planar aromatic compound with six carbon atoms forming a hexagonal ring and one hydrogen atom bonded to each carbon. Each carbon in the benzene ring is sp2 hybridized, and the molecule has alternating single and double bonds. However, all carbon-carbon bond lengths are found experimentally to be equal, which is because of the delocalization of electrons in the pi system.
02

Understanding resonance

Resonance is a concept used in Chemistry where a molecule or ion can be represented by several feasible Lewis structures (resonance forms). These resonance forms can contribute to an overall hybrid structure where the electrons are shared among all the atoms in the system. This hybrid structure, called the resonance hybrid, better describes the molecule's actual electron distribution than any single resonance form. In benzene, the electrons in the double bonds are delocalized, which means they are shared among all six carbon atoms, resulting in equal bond lengths for all C-C bonds.
03

Understanding aromaticity

Aromaticity is a property of cyclic, planar molecules, in which there is significant delocalization of π electrons following Hückel's rule (4n+2 π electrons, n being an integer). Aromatic compounds tend to be more stable than their non-aromatic counterparts, known as anti-aromatic compounds. Benzene is an aromatic compound because it has a planar ring, it is cyclic, and it follows Hückel's rule with 6 π electrons. Aromaticity does play a role in the resonance, delocalization, and overall stability of benzene.
04

Understanding hyperconjugation

Hyperconjugation is a phenomenon in which electrons from a neighboring σ bond and a π bond interact, providing increased stability to the molecule. This effect typically involves alkyl groups and their ability to stabilize carbocations. In the case of benzene, hyperconjugation is not the primary cause of equal bond lengths among C-C bonds.
05

Understanding tautomerism

Tautomerism is the chemical equilibrium between two different isomers of a compound, generally involving the movement of a hydrogen atom or a proton between different sites within the same molecule. It typically occurs in functional groups like ketones, aldehydes, and enol. Tautomerism is not relevant to the benzene structure, and therefore, it does not explain the observed bond length equality among C-C bonds.
06

Identifying the correct option

Based on the understanding of the four concepts, it becomes clear that resonance (option a) is the primary reason for the equal bond lengths in benzene. Aromaticity (option b) does contribute to benzene's stability and is related to resonance, but the resonance term is more directly associated with equal bond lengths. Options c and d, hyperconjugation and tautomerism, are not relevant to benzene's bond lengths. Therefore, the correct answer is: (a) resonance.

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Most popular questions from this chapter

The incorrect resonance structure of diazomethane is (a) \(\mathrm{H}_{2} \stackrel{\ominus}{\cdots}-\mathrm{N} \equiv \cdots\) (b) \(\mathrm{CH}_{3}-\mathrm{N}=\cdots \mathrm{N}\) (c) \(\mathrm{H}_{2} \mathrm{C}=\stackrel{\oplus}{\mathrm{N}}=\cdots \mathrm{N}^{\cdot}\) (d) \(\mathrm{H}_{2} \mathrm{C} \rightarrow \ddot{\mathrm{N}}=\cdots^{\ominus}\)

A carbocation can (a) dimerize (b) rearrange to give a more stable carbocation (c) eliminate a proton to give an alkene (d) add on to a nucleophile to form a stable compound

Stereoisomers are different from constitutional isomers in that the former differ from each other in the spatial arrangements while the latter differ on the basis of connectivity of atoms. The two compounds are related as (a) diastereomers (b) enantiomers (c) configurational isomers (d) two different compounds

In which of the following reactions, new chiral centre(s) is/are generated. (a) \(\mathrm{CH}_{3}-\mathrm{CH}=\mathrm{CH}-\mathrm{CH}_{3} \stackrel{\text { Baeyer'sreagent }}{\longrightarrow}\) (b) \(\mathrm{CH}_{3} \mathrm{CH}=\mathrm{CH}-\mathrm{CH}_{3}+\mathrm{HBr} \rightarrow\) (c) (d) \(\mathrm{CH}_{3}-\mathrm{CH}=\mathrm{CH}_{2}+\mathrm{HCl} \rightarrow\)

The specific arrangement of atoms that characterize a particular stereoisomer is known as (a) tautomer (b) conformation (c) configuration (d) geometry
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