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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Problem 53

Textbook Question

The nitrogen screened in purple in Figure 4.43 is not protonated at physiological pH. Why?
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Verified step by step guidance

Step 1: Identify the nitrogen atom in question (screened in purple in Figure 4.43) and note its chemical environment. This nitrogen is part of an amine group attached to a carbon chain.

Step 2: Consider the physiological pH, which is typically around 7.4. At this pH, amines are generally protonated due to their basic nature. However, the protonation depends on the electron density around the nitrogen atom.

Step 3: Analyze the inductive effects of nearby substituents. In this molecule, fluorine atoms are present near the nitrogen. Fluorine is highly electronegative and pulls electron density away from the nitrogen through the inductive effect, reducing the nitrogen's ability to accept a proton.

Step 4: Examine the resonance or steric effects. In this case, there is no significant resonance stabilization or steric hindrance directly affecting the nitrogen, but the reduced electron density due to the fluorine atoms makes the nitrogen less basic.

Step 5: Conclude that the nitrogen screened in purple is not protonated at physiological pH because the inductive effect of the fluorine atoms decreases its basicity, making it less likely to accept a proton under these conditions.

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Key Concepts

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

Protonation

Protonation is the addition of a proton (H+) to a molecule, which can significantly alter its chemical properties. In organic chemistry, the protonation state of a molecule can affect its reactivity, solubility, and interaction with other molecules. Understanding the conditions under which protonation occurs, such as pH levels, is crucial for predicting the behavior of nitrogen-containing compounds.

Physiological pH

Physiological pH typically refers to the pH of human blood, which is around 7.4. At this pH, certain functional groups, including amines, may exist in their deprotonated form, affecting their charge and reactivity. Recognizing the significance of physiological pH helps in understanding the protonation states of biomolecules in biological systems.

Basicity of Nitrogen

Nitrogen is a basic atom due to its lone pair of electrons, which can accept protons. However, the basicity can be influenced by the surrounding molecular environment and the presence of other functional groups. In the context of the question, the nitrogen's basicity at physiological pH determines whether it remains unprotonated, which is essential for understanding its role in biological molecules.

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