Table of contents

1. A Review of General Chemistry5h 5m
2. Molecular Representations1h 14m
3. Acids and Bases2h 46m
4. Alkanes and Cycloalkanes4h 17m
5. Chirality3h 39m
6. Thermodynamics and Kinetics1h 22m
7. Substitution Reactions1h 48m
8. Elimination Reactions2h 30m
9. Alkenes and Alkynes2h 9m
10. Addition Reactions3h 19m
11. Radical Reactions1h 58m
12. Alcohols, Ethers, Epoxides and Thiols2h 42m
13. Alcohols and Carbonyl Compounds2h 17m
14. Synthetic Techniques1h 26m
15. Analytical Techniques:IR, NMR, Mass Spect7h 3m
16. Conjugated Systems6h 13m
17. Ultraviolet Spectroscopy51m
18. Aromaticity2h 34m
19. Reactions of Aromatics: EAS and Beyond5h 1m
20. Phenols55m
21. Aldehydes and Ketones: Nucleophilic Addition4h 56m
22. Carboxylic Acid Derivatives: NAS2h 51m
23. The Chemistry of Thioesters, Phophate Ester and Phosphate Anhydrides1h 10m
24. Enolate Chemistry: Reactions at the Alpha-Carbon1h 53m
25. Condensation Chemistry2h 9m
26. Amines1h 43m
27. Heterocycles2h 0m
28. Carbohydrates5h 53m
29. Amino Acids4h 20m
30. Peptides and Proteins2h 42m
31. Catalysis in Organic Reactions1h 30m
32. Lipids 2h 50m
33. The Organic Chemistry of Metabolic Pathways2h 52m
34. Nucleic Acids1h 32m
35. Transition Metals6h 14m
36. Synthetic Polymers1h 49m

18. Aromaticity

Aromatic Heterocycles

Organic Chemistry

18. Aromaticity

Aromatic Heterocycles

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6:18 minutes

Problem 19a,b,c

Textbook Question

Explain why each compound is aromatic, antiaromatic, or nonaromatic.
(a)
(b)
(c)

Verified step by step guidance

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

Step 2: Analyze compound (a). The structure is cyclic and planar, with conjugated π-electrons. Count the π-electrons in the ring, including lone pairs on heteroatoms that can participate in conjugation. Apply Hückel's rule to determine if it is aromatic, antiaromatic, or nonaromatic.

Step 3: Analyze compound (b). The structure is cyclic and planar, with conjugated π-electrons. Count the π-electrons in the ring, including lone pairs on heteroatoms that can participate in conjugation. Apply Hückel's rule to determine if it is aromatic, antiaromatic, or nonaromatic.

Step 4: Analyze compound (c). The structure is cyclic and planar, with conjugated π-electrons. Count the π-electrons in the ring, including lone pairs on heteroatoms that can participate in conjugation. Apply Hückel's rule to determine if it is aromatic, antiaromatic, or nonaromatic.

Step 5: Summarize the findings for each compound based on the analysis. Compound (a), (b), and (c) can be classified as aromatic, antiaromatic, or nonaromatic depending on whether they meet the criteria outlined in Step 1.

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Key Concepts

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

Aromaticity

Aromaticity refers to the property of cyclic compounds that exhibit enhanced stability due to delocalized π electrons. For a compound to be aromatic, it must be cyclic, planar, fully conjugated, and follow Hückel's rule, which states that it should have 4n + 2 π electrons, where n is a non-negative integer. This delocalization leads to lower energy and increased stability compared to non-aromatic compounds.

Antiaromaticity

Antiaromaticity is the opposite of aromaticity and describes cyclic compounds that are destabilized due to the presence of 4n π electrons, which leads to increased energy and instability. For a compound to be classified as antiaromatic, it must be cyclic, planar, and fully conjugated, but it fails to meet Hückel's rule. This instability often results in a higher reactivity compared to both aromatic and non-aromatic compounds.

Nonaromatic Compounds

Nonaromatic compounds are those that do not meet the criteria for aromaticity or antiaromaticity. These compounds can be acyclic, lack full conjugation, or be non-planar, which prevents the delocalization of π electrons. As a result, nonaromatic compounds do not exhibit the unique stability associated with aromatic compounds and typically have reactivity patterns similar to aliphatic compounds.

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