Chapter 34: Problem 2
Draw the structures of (a) pyridine, (b) indole, (c) the pyrylium cation and (d) imidazole.
Short Answer
Expert verified
Pyridine: a six-membered ring with one nitrogen; Indole: benzene fused to pyrrole; Pyrylium cation: six-membered ring with one oxygen cation; Imidazole: five-membered ring with two nitrogens.
Step by step solution
01
Understanding the structure of Pyridine
Pyridine is a basic heterocyclic compound with the chemical formula \( C_5H_5N \). It resembles benzene but with one CH group replaced by a nitrogen atom. This means it has a six-membered ring with alternating pi bonds (double bonds) around the ring.
02
Drawing the structure of Pyridine
To draw pyridine, start with a hexagonal ring (like benzene). Place one nitrogen atom in the ring, and then alternate pi bonds around the ring. Each vertex not occupied by the nitrogen is occupied by a carbon atom, making five carbon atoms in total.
03
Understanding the structure of Indole
Indole is a bicyclic structure consisting of a benzene ring fused to a five-membered nitrogen-containing pyrrole ring. The chemical formula is \( C_8H_7N \). The pyrrole ring contributes to the aromatic system with one nitrogen atom.
04
Drawing the structure of Indole
To draw indole, begin with a benzene ring. Adjacent to it, create a five-membered ring sharing two of the carbon atoms with the benzene. Place a nitrogen atom in this five-membered ring and add double bonds in the pyrrole pattern within this smaller ring.
05
Understanding the structure of the Pyrylium Cation
The pyrylium cation is an aromatic compound with the formula \( C_5H_5O^+ \). Like pyridine, it has a six-membered ring but with a positively charged oxygen atom instead of nitrogen.
06
Drawing the structure of the Pyrylium Cation
For the pyrylium cation, draw a six-membered ring similar to pyridine. Replace the nitrogen atom with an oxygen atom carrying a positive charge and consistent with alternating double bonds around the ring.
07
Understanding the structure of Imidazole
Imidazole is a five-membered planar ring with the chemical formula \( C_3H_4N_2 \). It comprises two nitrogen atoms at non-adjacent positions within the ring.
08
Drawing the structure of Imidazole
To draw imidazole, construct a five-membered ring. Insert two nitrogen atoms such that they are separated by one carbon. Place the pi bonds so that they contribute to an aromatic system, alternating within the ring around the nitrogen atoms.
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Key Concepts
These are the key concepts you need to understand to accurately answer the question.
Pyridine
Pyridine is a fascinating member of the heterocyclic compound family, renowned for its unique structure and properties. Its structure is similar to benzene, yet distinctly different due to the incorporation of a nitrogen atom in place of one carbon atom. This nitrogen atom plays a crucial role in defining pyridine’s basicity and function in chemical reactions.
The aromatic ring of pyridine consists of six members, with the molecular formula of pyridine being \( C_5H_5N \). The presence of alternating pi bonds within this ring contributes to its stability and aromatic character. These alternating double bonds also enhance the compound's ability to participate in electrophilic substitution reactions.
Pyridine’s utility extends across various applications, including as a precursor to agrochemical, pharmaceutical, and vitamin synthesis. Its nitrogen atom offers a lone pair of electrons, making pyridine a powerful nucleophile and also a weak base typically used in deprotonation reactions.
The aromatic ring of pyridine consists of six members, with the molecular formula of pyridine being \( C_5H_5N \). The presence of alternating pi bonds within this ring contributes to its stability and aromatic character. These alternating double bonds also enhance the compound's ability to participate in electrophilic substitution reactions.
Pyridine’s utility extends across various applications, including as a precursor to agrochemical, pharmaceutical, and vitamin synthesis. Its nitrogen atom offers a lone pair of electrons, making pyridine a powerful nucleophile and also a weak base typically used in deprotonation reactions.
Indole
Indole, a compound that seamlessly combines complexity and stability, provides a captivating insight into the world of bicyclic structures. Indole is characterized by its fusion of a six-membered benzene ring with a five-membered pyrrole ring, resulting in a structure known for its aromaticity and stability.
In indole's molecular formula, \( C_8H_7N \), the benzene and pyrrole rings share two carbon atoms. This sharing leads to a blended π-electron cloud across the entire molecule, reinforcing its aromatic character. The nitrogen atom in the pyrrole part contributes to the aromatic system, participating in resonance and electron distribution.
Notably, indole is critically important in nature and chemistry. It serves as a fundamental building block in a variety of natural substances, including tryptophan, an essential amino acid. Additionally, indole derivatives are found in pharmaceuticals and are central to the structure of many bioactive molecules.
In indole's molecular formula, \( C_8H_7N \), the benzene and pyrrole rings share two carbon atoms. This sharing leads to a blended π-electron cloud across the entire molecule, reinforcing its aromatic character. The nitrogen atom in the pyrrole part contributes to the aromatic system, participating in resonance and electron distribution.
Notably, indole is critically important in nature and chemistry. It serves as a fundamental building block in a variety of natural substances, including tryptophan, an essential amino acid. Additionally, indole derivatives are found in pharmaceuticals and are central to the structure of many bioactive molecules.
Pyrylium Cation
The pyrylium cation offers a curious twist on aromatic chemistry with its unique positively charged nature. With the chemical formula \( C_5H_5O^+ \), it displays characteristics that are both intriguing and useful in various chemical landscapes.
Structurally, the pyrylium cation bears similarity to pyridine. Both form a six-membered ring. However, the presence of a positively charged oxygen atom replaces the nitrogen found in pyridine. This positional change transforms it into a vibrant participant in electrophilic reactions due to the electron-deficient nature caused by the positive charge.
The aromatic stability of the pyrylium cation arises from its cyclic conjugation and the delocalization of electrons in the ring. This allows it to engage actively in certain chemical transformations, where the positive charge facilitates interactions that are not typically feasible in neutral heterocycles.
Structurally, the pyrylium cation bears similarity to pyridine. Both form a six-membered ring. However, the presence of a positively charged oxygen atom replaces the nitrogen found in pyridine. This positional change transforms it into a vibrant participant in electrophilic reactions due to the electron-deficient nature caused by the positive charge.
The aromatic stability of the pyrylium cation arises from its cyclic conjugation and the delocalization of electrons in the ring. This allows it to engage actively in certain chemical transformations, where the positive charge facilitates interactions that are not typically feasible in neutral heterocycles.
Imidazole
Imidazole stands out as a five-membered heterocycle with notable properties important in both biochemistry and industrial chemistry. Its structure, \( C_3H_4N_2 \), is defined by the presence of two non-adjacent nitrogen atoms within the ring, which strongly influence its chemical behavior.
This aromatic compound features a distinct electron distribution, where the nitrogen atoms at distinct positions create a dipole. The alternating pi bonds contribute to its aromaticity as each nitrogen participates in the electron delocalization.
Applications of imidazole are diverse, from serving as a part of the histidine amino acid in enzyme active sites to functioning as a ligand in coordination chemistry. Moreover, imidazole frameworks are integral in pharmaceuticals, contributing to the activity of many antifungal and antibacterial drugs. The compound's ability to act as a weak base and donor of hydrogen bonds plays a significant role in its applications and stability under varied conditions.
This aromatic compound features a distinct electron distribution, where the nitrogen atoms at distinct positions create a dipole. The alternating pi bonds contribute to its aromaticity as each nitrogen participates in the electron delocalization.
Applications of imidazole are diverse, from serving as a part of the histidine amino acid in enzyme active sites to functioning as a ligand in coordination chemistry. Moreover, imidazole frameworks are integral in pharmaceuticals, contributing to the activity of many antifungal and antibacterial drugs. The compound's ability to act as a weak base and donor of hydrogen bonds plays a significant role in its applications and stability under varied conditions.
