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

Basicity of Aromatic Heterocycles

Organic Chemistry

18. Aromaticity

Basicity of Aromatic Heterocycles

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4:03 minutes

Problem 35f

Textbook Question

Some of the following compounds show aromatic properties, and others do not.
1. Predict which ones are likely to be aromatic, and explain why they are aromatic.
2. Predict which nitrogen atoms are more basic than water and which are less basic.
(f)

Verified step by step guidance

Step 1: Analyze the structure of the compound provided. The image shows a six-membered ring with alternating double bonds (a conjugated system) and a positively charged nitrogen atom with a hydrogen attached. This structure resembles pyridinium.

Step 2: Determine aromaticity using Huckel's rule. Huckel's rule states that a compound is aromatic if it is cyclic, planar, fully conjugated, and contains (4n + 2) π electrons, where n is an integer. Count the π electrons in the conjugated system of the ring.

Step 3: Evaluate the π electron count. The ring has three double bonds, contributing 6 π electrons. Since 6 π electrons satisfy Huckel's rule (4n + 2, where n = 1), the compound is aromatic.

Step 4: Assess the basicity of the nitrogen atom. The nitrogen in pyridinium is positively charged, which significantly reduces its ability to donate electrons. Therefore, this nitrogen is less basic than water.

Step 5: Summarize the findings. The compound is aromatic due to its cyclic, planar, conjugated structure and 6 π electrons. The nitrogen atom is less basic than water because it is positively charged and unable to effectively donate electrons.

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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 special stability and unique properties of cyclic compounds that follow Hückel's rule, which states that a molecule must have (4n + 2) π electrons, where n is a non-negative integer. Aromatic compounds are typically planar, fully conjugated, and exhibit resonance, leading to lower reactivity compared to non-aromatic compounds. The presence of a nitrogen atom in a ring can influence aromaticity depending on its hybridization and the electron density it contributes.

Basicity of Nitrogen

The basicity of nitrogen atoms in organic compounds is determined by their ability to donate a lone pair of electrons. Factors such as hybridization, electronegativity, and the presence of electron-withdrawing or electron-donating groups affect basicity. In general, sp3-hybridized nitrogen is more basic than sp2-hybridized nitrogen due to the greater availability of the lone pair for protonation, while aromatic nitrogen can be less basic if it participates in the aromatic system.

Hückel's Rule

Hückel's rule is a criterion for determining the aromaticity of cyclic compounds. It states that a planar, cyclic molecule must have a total of (4n + 2) π electrons in its conjugated system to be considered aromatic. This rule helps predict the stability and reactivity of compounds, as aromatic systems are generally more stable than their non-aromatic counterparts. Understanding this rule is essential for evaluating the aromatic nature of the compounds in the question.

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Ciprofloxacin is a member of the fluoroquinolone class of antibiotics.

(b) Which nitrogen atoms are basic?

Textbook Question

Ciprofloxacin is a member of the fluoroquinolone class of antibiotics.

a. Which of its rings are aromatic?

Textbook Question

Some of the following compounds show aromatic properties, and others do not.

1. Predict which ones are likely to be aromatic, and explain why they are aromatic.

2. Predict which nitrogen atoms are more basic than water and which are less basic.

(d)

Textbook Question

Some of the following compounds show aromatic properties, and others do not.

1. Predict which ones are likely to be aromatic, and explain why they are aromatic.

2. Predict which nitrogen atoms are more basic than water and which are less basic.

(e)

Textbook Question

Some of the following compounds show aromatic properties, and others do not.

1. Predict which ones are likely to be aromatic, and explain why they are aromatic.

2. Predict which nitrogen atoms are more basic than water and which are less basic.

(m)

Multiple Choice

Why is II a weaker base than I?

Textbook Question

Each of the following heterocycles includes one or more nitrogen atoms. Classify each nitrogen atom as strongly basic or weakly basic, according to the availability of its lone pair of electrons.

(d)

(e)

Textbook Question

Each of the following heterocycles includes one or more nitrogen atoms. Classify each nitrogen atom as strongly basic or weakly basic, according to the availability of its lone pair of electrons.

(a)

(b)

(c)

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