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

3. Acids and Bases

Ranking Acidity

Organic Chemistry

3. Acids and Bases

Ranking Acidity

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5:54 minutes

Problem 82

Textbook Question

Purine is a heterocyclic compound with four nitrogen atoms.
a. Which nitrogen is most apt to be protonated?
b. Which nitrogen is least apt to be protonated?

Verified step by step guidance

Step 1: Understand the structure of purine. Purine is a bicyclic heterocyclic compound composed of a pyrimidine ring fused to an imidazole ring. It contains four nitrogen atoms, each with different electronic environments.

Step 2: Analyze the electronic environment of each nitrogen atom. The nitrogen atoms in purine can be classified as either sp2-hybridized or sp3-hybridized, and their ability to be protonated depends on factors such as lone pair availability and resonance stabilization.

Step 3: Determine which nitrogen is most apt to be protonated. The nitrogen atom with the most available lone pair and least steric hindrance, and which contributes least to resonance stabilization, is the most likely to be protonated.

Step 4: Determine which nitrogen is least apt to be protonated. The nitrogen atom whose lone pair is involved in resonance or aromaticity, or is sterically hindered, is the least likely to be protonated.

Step 5: Apply these principles to purine's structure. Examine the resonance structures and aromaticity of purine to identify the nitrogen atoms most and least apt to be protonated. Consider the role of each nitrogen in maintaining the aromatic stability of the molecule.

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Key Concepts

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

Protonation and Basicity

Protonation refers to the addition of a proton (H+) to a molecule, which often occurs at basic sites. In heterocyclic compounds like purines, the basicity of nitrogen atoms varies due to their electronic environment. The nitrogen atom that can best stabilize the positive charge after protonation is considered the most basic and thus the most likely to be protonated.

Heterocyclic Compounds

Heterocyclic compounds are cyclic structures that contain atoms of at least two different elements in their rings, commonly carbon and nitrogen. In purines, the presence of multiple nitrogen atoms influences their chemical properties, including acidity and basicity. Understanding the structure of these compounds is crucial for predicting their reactivity and interactions.

Acidity and Basicity of Nitrogen Atoms

The acidity and basicity of nitrogen atoms in a heterocyclic compound depend on their hybridization and the presence of electron-withdrawing or electron-donating groups. In the context of purines, the nitrogen atoms can exhibit different levels of acidity and basicity, affecting their likelihood of being protonated. This concept is essential for determining which nitrogen is most or least likely to accept a proton.

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