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 Hydrocarbons

Organic Chemistry

18. Aromaticity

Aromatic Hydrocarbons

Previous problemNext problem

5:23 minutes

Problem 32c

Textbook Question

The following molecules and ions are grouped by similar structures. Classify each as aromatic, antiaromatic, or nonaromatic. For the aromatic and antiaromatic species, give the number of pi electrons in the ring.
(c)

Verified step by step guidance

Step 1: Analyze the structure of each molecule or ion. Determine whether the ring is cyclic, planar, and conjugated (i.e., has alternating single and double bonds or lone pairs that can participate in resonance). These are prerequisites for aromaticity or antiaromaticity.

Step 2: Apply Hückel's rule for aromaticity, which states that a molecule is aromatic if it has (4n + 2) π electrons, where n is a non-negative integer. Count the π electrons in the ring for each structure.

Step 3: For antiaromatic species, check if the molecule has 4n π electrons, which leads to instability due to electron repulsion. If neither (4n + 2) nor 4n π electrons are present, the molecule is nonaromatic.

Step 4: For each structure, consider the effect of substituents (e.g., lone pairs, charges) on the π electron count. For example, a negatively charged substituent may contribute two π electrons, while a positively charged substituent may remove electrons from the π system.

Step 5: Classify each structure as aromatic, antiaromatic, or nonaromatic based on the π electron count and the criteria above. For aromatic and antiaromatic species, specify the number of π electrons in the ring.

Verified video answer for a similar problem:

This video solution was recommended by our tutors as helpful for the problem above

Video duration:

Play a video:

Was this helpful?

Key Concepts

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

Aromaticity

Aromatic compounds are cyclic, planar molecules with a ring of p-orbitals that allows for delocalization of pi electrons. According to Hückel's rule, a molecule is aromatic if it contains 4n + 2 pi electrons, where n is a non-negative integer. This delocalization contributes to the stability and unique reactivity of aromatic compounds.

Antiaromaticity

Antiaromatic compounds are also cyclic and planar but contain 4n pi electrons, which leads to instability due to the unfavorable electron delocalization. This instability results in higher reactivity compared to nonaromatic compounds. Understanding the distinction between aromatic and antiaromatic systems is crucial for predicting the behavior of these molecules.

Nonaromaticity

Nonaromatic compounds do not meet the criteria for aromaticity or antiaromaticity. They may be acyclic, lack planarity, or have an insufficient number of pi electrons for delocalization. Nonaromatic compounds typically exhibit standard reactivity patterns and do not benefit from the stability associated with aromatic systems.

Previous problemNext problem

4:52m

Watch next

Master Aromaticity of Hydrocarbons with a bite sized video explanation from Johnny

Start learning