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

Previous problemNext problem

2:34 minutes

Problem 35m

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)

Verified step by step guidance

Step 1: Analyze the structure of the compound provided. The compound is a nitrogen-containing heterocyclic ring with alternating double bonds, which suggests it may exhibit aromatic properties. Aromaticity is determined by the Huckel rule, which states that a compound must have (4n + 2) π-electrons to be aromatic.

Step 2: Count the π-electrons in the ring. Each double bond contributes 2 π-electrons, and the nitrogen atom may contribute a lone pair of electrons if it is part of the conjugated system. Verify if the total number of π-electrons satisfies the Huckel rule.

Step 3: Determine if the nitrogen atom's lone pair is part of the conjugated π-system. If the lone pair is in an sp2 orbital and overlaps with the π-system, it contributes to aromaticity. If the lone pair is in an sp3 orbital, it does not contribute to aromaticity.

Step 4: Evaluate the basicity of the nitrogen atom. Nitrogen atoms are more basic when their lone pair is readily available for protonation. If the lone pair is delocalized in the aromatic π-system, the nitrogen is less basic than water. If the lone pair is localized, the nitrogen is more basic than water.

Step 5: Conclude the aromaticity and basicity of the compound based on the above analysis. If the compound satisfies the Huckel rule and the nitrogen's lone pair contributes to the π-system, it is aromatic. If the nitrogen's lone pair is localized, it is more basic than water; otherwise, it is less basic.

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

Aromaticity refers to the special stability and unique properties of cyclic compounds that follow Hückel's rule, which states that a compound 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. Common examples include benzene and pyridine.

Basicity of Nitrogen

The basicity of nitrogen atoms in organic compounds is influenced by their hybridization and the presence of electron-donating or withdrawing groups. Nitrogen in sp3 hybridization (like in amines) is generally more basic than in sp2 (like in pyridine) due to the availability of the lone pair for protonation. The basicity can also be compared to water, where nitrogen atoms that can stabilize the positive charge after protonation are considered more basic.

Heterocycles

Heterocycles are cyclic compounds that contain at least one atom other than carbon in the ring, such as nitrogen, oxygen, or sulfur. The presence of heteroatoms can significantly affect the chemical properties, including aromaticity and basicity. For instance, nitrogen in a heterocyclic aromatic compound can participate in resonance, influencing both its stability and its ability to accept protons, thus affecting its basicity.

Watch next

Master Heterocycles - Which lone pairs react? with a bite sized video explanation from Johnny

Start learning

Related Videos

Related Practice

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.

(f)

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)

Textbook Question

Explain why, when the imidazole ring of histidine is protonated, the double-bonded nitrogen is the nitrogen that accepts the proton.

Show more practices