Ch. 8 - Delocalized Electrons: Their Effect on Stability, pKa, and the Products of a Reaction • Aromaticity and Electronic Effects: An Introduction to the Reactions of Benzene

Bruice8th EditionOrganic ChemistryISBN: 9780135213711Not the one you use?Change textbook

Bruice 8th Edition

Ch. 8 - Delocalized Electrons: Their Effect on Stability, pKa, and the Products of a Reaction • Aromaticity and Electronic Effects: An Introduction to the Reactions of Benzene

Problem 48b

Chapter 9, Problem 48b

Which of the following are aromatic?
d.
e.
f.

Verified step by step guidance

Step 1: Recall the criteria for aromaticity. A molecule is aromatic if it satisfies the following conditions: (1) It is cyclic, (2) It is planar, (3) It has a conjugated π-electron system (alternating single and double bonds), and (4) It follows Huckel's rule, which states that the molecule must have (4n + 2) π-electrons, where n is a non-negative integer.

Step 2: Analyze structure A. Structure A is a cyclic molecule with alternating single and double bonds, indicating conjugation. It has a negative charge, which contributes two π-electrons to the system. Count the total π-electrons in the ring, including those from the double bonds and the negative charge, and check if it satisfies Huckel's rule.

Step 3: Analyze structure B. Structure B is a cyclic molecule with alternating single and double bonds, indicating conjugation. It has a positive charge, which removes one π-electron from the system. Count the total π-electrons in the ring, including those from the double bonds and the positive charge, and check if it satisfies Huckel's rule.

Step 4: Analyze structure C. Structure C is a cyclic molecule with alternating single and double bonds, indicating conjugation. Count the total π-electrons in the ring from the double bonds and check if it satisfies Huckel's rule.

Step 5: Compare the results for structures A, B, and C. Determine which structures satisfy all the criteria for aromaticity, including Huckel's rule, and identify them as aromatic.

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Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

Aromaticity

Aromaticity is a property of cyclic compounds that exhibit enhanced stability due to the delocalization of π electrons across the ring. For a compound to be aromatic, it must be cyclic, planar, and follow Hückel's rule, which states that it should have 4n + 2 π electrons, where n is a non-negative integer.

Hückel's Rule

Hückel's rule is a criterion used to determine if a planar, cyclic compound is aromatic. According to this rule, a compound is aromatic if it contains a total of 4n + 2 π electrons in its conjugated system, which leads to increased stability and unique chemical properties compared to non-aromatic compounds.

Planarity and Conjugation

For a compound to be aromatic, it must be planar, allowing for effective overlap of p orbitals, which facilitates the delocalization of π electrons. Conjugation refers to the alternating single and double bonds that allow for this electron delocalization, contributing to the overall stability and reactivity of the aromatic system.

Which of the following are aromatic? d. e. f.