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Ch. 23 - Benzene 1: Aromatic Stability and Substitution Reactions
Mullins - Organic Chemistry: A Learner Centered Approach 1st Edition
Mullins1st EditionOrganic Chemistry: A Learner Centered ApproachISBN: 9780137566471당신이 사용하는 게 아니라요?교과서 변경
모든 교과서Mullins 1st EditionCh. 23 - Benzene 1: Aromatic Stability and Substitution Reactions문제 13
22장, 문제 13

Cyclopentane has pKₐ = 50, whereas cyclopentadiene has pKₐ = 16. Explain this difference.
Structural formulas of cyclopentane and cyclopentadiene with their pKₐ values, 50 and 16, respectively.

검증된 단계별 안내
1
Identify the structures of cyclopentane and cyclopentadiene. Cyclopentane is a saturated hydrocarbon with no double bonds, while cyclopentadiene contains two conjugated double bonds.
Understand the concept of pKₐ, which is a measure of the acidity of a compound. A lower pKₐ value indicates a stronger acid.
Consider the stability of the conjugate base formed after deprotonation. Cyclopentadiene, when deprotonated, forms a cyclopentadienyl anion, which is aromatic and highly stabilized by resonance.
Recognize that cyclopentane, when deprotonated, forms a non-aromatic anion with no resonance stabilization, making it a much weaker acid compared to cyclopentadiene.
Conclude that the significant difference in pKₐ values is due to the aromatic stabilization of the cyclopentadienyl anion, which is absent in the cyclopentane anion.

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주요 개념

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pKa and Acidity

The pKa value is a measure of the acidity of a compound, indicating how easily a compound donates a proton (H+). A lower pKa value corresponds to a stronger acid, meaning it more readily donates a proton. In this context, cyclopentadiene with a pKa of 16 is a much stronger acid than cyclopentane, which has a pKa of 50, indicating a significant difference in their acidity.
추천 영상:
07:45
Identifying pKa values

Aromaticity and Stability

Aromaticity refers to the increased stability of a compound due to the delocalization of electrons in a conjugated pi system. Cyclopentadiene can form an aromatic anion upon losing a proton, as it achieves a stable, aromatic 6 pi-electron system. This stability significantly lowers its pKa compared to cyclopentane, which lacks such stabilization.
추천 영상:
08:19
Intro to Aromaticity

Conjugation and Resonance

Conjugation involves the overlap of p-orbitals across adjacent atoms, allowing for electron delocalization. In cyclopentadiene, the presence of conjugated double bonds allows for resonance stabilization of the resulting anion after deprotonation. This resonance stabilization is absent in cyclopentane, contributing to its much higher pKa value.
추천 영상:
05:29
Definition of Conjugation
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교과서 질문

(i) Classify the following molecules as aromatic, nonaromatic, or antiaromatic.

(ii) For the aromatic and antiaromatic molecules, solve for n in Hückel’s/Breslow’s rule. For the other molecules, explain which of the rules of aromaticity is being broken.

(d)

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Imidazole is a heteroaromatic base. Which nitrogen, a or b, is most basic?

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교과서 질문

(i) Classify the following molecules as aromatic, nonaromatic, or antiaromatic.

(ii) For the aromatic and antiaromatic molecules, solve for n in Hückel’s/Breslow’s rule. For the other molecules, explain which of the rules of aromaticity is being broken.

(b)

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교과서 질문

Between pyrrole and pyrrolidine, which nitrogen would be most nucleophilic? Why?

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교과서 질문

Which resonance structure, A or B, is most contributing?

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교과서 질문

Which of the following concerted reactions would have a more stable transition state? Why?

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