Domanda del libro di testo
The chemical shifts of the C-2 hydrogen in the spectra of pyrrole, pyridine, and pyrrolidine are 2.82 ppm, 6.42 ppm, and 8.50 ppm. Match each heterocycle with its chemical shift.
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Ch. 19 - More About Amines • Reactions of Heterocyclic Compounds
Bruice8th EditionOrganic ChemistryISBN: 9780135213711
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TOC.tableOfContents
- Ch. 1 - Remembering General Chemistry: Electronic Structure and Bonding31
- Ch. 2 - Acids and Bases: Central to Understanding Organic Chemistry84
- Ch. 3 - An Introduction to Organic Compounds: Nomenclature, Physical Properties, and Structure183
- Ch. 4 - Isomers: The Arrangement of Atoms in Space121
- Ch. 5 - Alkenes: Structure, Nomenclature, and an Introduction to Reactivity • Thermodynamics and Kinetics83
- Ch. 6 - The Reactions of Alkenes • The Stereochemistry of Addition Reactions175
- Ch. 7 - The Reactions of Alkynes • An Introduction to Multistep Synthesis119
- Ch. 8 - Delocalized Electrons: Their Effect on Stability, pKa, and the Products of a Reaction • Aromaticity and Electronic Effects: An Introduction to the Reactions of Benzene148
- Ch. 9 - Substitution and Elimination Reactions of Alkyl Halides212
- Ch. 10 - Reactions of Alcohols, Ethers, Epoxides, Amines, and Sulfur-Containing Compounds131
- Ch. 11 - Organometallic Compounds60
- Ch. 12 - Radicals90
- Ch. 13 - Mass Spectrometry; Infrared Spectroscopy; UV/Vis Spectroscopy62
- Ch. 14 - NMR Spectroscopy95
- Ch. 15 - Reactions of Carboxylic Acids and Carboxylic Acid Derivatives123
- Ch. 16 - Reactions of Aldehydes and Ketones • More Reactions of Carboxylic Acid Derivatives141
- Ch. 17 - Reactions at the Alpha-Carbon101
- Ch. 18 - Reactions of Benzene and Substituted Benzenes144
- Ch. 19 - More About Amines • Reactions of Heterocyclic Compounds49
- Ch. 20 - The Organic Chemistry of Carbohydrates80
- Ch. 21 - Amino Acids, Peptides, and Proteins57
- Ch. 22 - Catalysis in Organic Reactions and in Enzymatic Reactions35
- Ch. 23 - The Organic Chemistry of the Coenzymes—Compounds Derived from Vitamins1
- Ch. 28 - Pericyclic Reactions58
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Bruice 8th EditionCh. 19 - More About Amines • Reactions of Heterocyclic CompoundsProblema 36
Bruice 8th EditionCh. 19 - More About Amines • Reactions of Heterocyclic CompoundsProblema 36Capitolo 19, Problema 36
Explain why pyrrole (pKa ~ 17) is a much stronger acid than ammonia (pKa = 36).
Guida verificata passo dopo passo1
Step 1: Understand the concept of pKa. The pKa value is a measure of the acidity of a compound. A lower pKa value indicates a stronger acid, meaning the compound is more likely to donate a proton (H⁺).
Step 2: Compare the structures of pyrrole and ammonia. Pyrrole is an aromatic heterocyclic compound with a nitrogen atom in a five-membered ring, while ammonia (NH₃) is a simple molecule with a lone pair of electrons on nitrogen.
Step 3: Analyze the conjugate bases formed after deprotonation. When pyrrole loses a proton, the negative charge on nitrogen can delocalize into the aromatic ring, stabilizing the conjugate base through resonance. In contrast, ammonia's conjugate base (NH₂⁻) does not have resonance stabilization.
Step 4: Consider the role of aromaticity. Pyrrole is aromatic, and the delocalization of electrons in the ring contributes to its stability. The ability to maintain aromaticity after deprotonation further stabilizes pyrrole's conjugate base, making pyrrole a stronger acid.
Step 5: Evaluate the electronegativity and hybridization of nitrogen. In pyrrole, the nitrogen is sp² hybridized and part of the aromatic system, which affects its ability to donate a proton. In ammonia, the nitrogen is sp³ hybridized, and the lack of resonance stabilization makes it less acidic.
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Acidity and pKa
Acidity is a measure of a compound's ability to donate protons (H+ ions). The pKa value quantifies this ability, with lower pKa values indicating stronger acids. Pyrrole, with a pKa of ~17, is significantly more acidic than ammonia, which has a pKa of 36, meaning pyrrole can more readily donate a proton compared to ammonia.
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07:45
Identifying pKa values
Resonance Stabilization
Resonance stabilization occurs when a molecule can distribute its electron density across multiple structures, lowering its energy. In pyrrole, the negative charge formed after deprotonation can be delocalized over the nitrogen and the adjacent carbon atoms, stabilizing the conjugate base. This stabilization is not present in ammonia, making pyrrole a stronger acid.
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03:43The radical stability trend.
Aromaticity
Aromaticity refers to the enhanced stability of cyclic compounds with conjugated pi electron systems that follow Huckel's rule. Pyrrole is an aromatic compound, which contributes to its stability after losing a proton. In contrast, ammonia is not aromatic, and thus lacks this additional stabilization, further explaining the difference in acidity between the two compounds.
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08:19Intro to Aromaticity
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