Textbook Question
Why is imidazole a stronger acid (pKa ~ 14.4) than pyrrole (pKa ~ 17)?
2
views
Ch. 19 - More About Amines • Reactions of Heterocyclic Compounds
Bruice8th EditionOrganic ChemistryISBN: 9780135213711
Not the one you use?Change textbookSelect a different textbook
Table of contents
- Ch. 1 - Remembering General Chemistry: Electronic Structure and Bonding (Part 1)31
- Ch. 1 - Remembering General Chemistry: Electronic Structure and Bonding (Part 2)65
- 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
All textbooks
Bruice 8th EditionCh. 19 - More About Amines • Reactions of Heterocyclic CompoundsProblem 15
Bruice 8th EditionCh. 19 - More About Amines • Reactions of Heterocyclic CompoundsProblem 15Chapter 20, Problem 15
Rank imidazole, pyrrole, and benzene from most reactive to least reactive toward electrophilic aromatic substitution.
Verified step by step guidance1
Understand the concept of electrophilic aromatic substitution (EAS): This reaction involves the replacement of a hydrogen atom on an aromatic ring with an electrophile. The reactivity of the aromatic compound depends on the electron density of the ring, which is influenced by the substituents or heteroatoms present in the structure.
Analyze the structure of imidazole: Imidazole contains two nitrogen atoms in a five-membered aromatic ring. One nitrogen has a lone pair that participates in the aromaticity of the ring, while the other nitrogen has a lone pair that is not involved in aromaticity. This makes imidazole electron-rich and highly reactive toward electrophiles.
Analyze the structure of pyrrole: Pyrrole is a five-membered aromatic ring with one nitrogen atom. The lone pair on the nitrogen is delocalized into the aromatic system, increasing the electron density of the ring. However, it is slightly less electron-rich compared to imidazole because it has only one nitrogen contributing to the electron density.
Analyze the structure of benzene: Benzene is a six-membered aromatic ring with no heteroatoms. Its electron density is evenly distributed across the ring, making it less reactive toward electrophiles compared to imidazole and pyrrole.
Rank the compounds based on their reactivity: Since imidazole has the highest electron density due to the presence of two nitrogen atoms, it is the most reactive. Pyrrole, with one nitrogen atom, is less reactive than imidazole but more reactive than benzene. Benzene, with no heteroatoms, is the least reactive. Therefore, the order of reactivity is: imidazole > pyrrole > benzene.
Verified video answer for a similar problem:
This video solution was recommended by our tutors as helpful for the problem above.
Was this helpful?
Key Concepts
Here are the essential concepts you must grasp in order to answer the question correctly.
Electrophilic Aromatic Substitution (EAS)
Electrophilic Aromatic Substitution is a fundamental reaction in organic chemistry where an electrophile replaces a hydrogen atom on an aromatic ring. The reactivity of the aromatic compound is influenced by the electron density of the ring, which is affected by substituents. Understanding EAS is crucial for ranking the reactivity of compounds like imidazole, pyrrole, and benzene.
Recommended video:
Guided course
03:07
EAS Review
Aromaticity and Electron Density
Aromatic compounds are characterized by their stable ring structure and delocalized π-electrons, which contribute to their unique reactivity. The electron density on the ring determines how readily it can react with electrophiles. Compounds with higher electron density are generally more reactive in EAS, making the concept of aromaticity essential for comparing imidazole, pyrrole, and benzene.
Recommended video:
Guided course
08:19Intro to Aromaticity
Substituent Effects
The presence of different substituents on an aromatic ring can significantly influence its reactivity toward electrophiles. Electron-donating groups increase electron density and enhance reactivity, while electron-withdrawing groups decrease it. In the case of imidazole, pyrrole, and benzene, understanding how their structures affect electron donation is key to ranking their reactivity in EAS.
Recommended video:
2:02Directing Effects in Substituted Pyrroles, Furans, and Thiophenes Concept 1
Related Practice
Textbook Question
Imidazole boils at 257 °C, whereas N-methylimidazole boils at 199 °C. Explain the difference in boiling points.
2
views
Textbook Question
Propose a mechanism for the following reaction:
1
views
Textbook Question
What other product is formed in this reaction?
1
views
Textbook Question
Rank the following compounds from easiest to hardest at removing a proton from its methyl substituent:
2
views
Textbook Question
What percent of imidazole is protonated at physiological pH (7.4)?
2
views