Introduces heterocyclic compounds with one heteroatom, then covers pyridine's structure, aromaticity and basicity, its electrophilic and nucleophilic substitution and N-alkylation. It goes on to nicotinamide (vitamin B3), NAD and its redox role, nicotine's pyridine and pyrrolidine rings, and vitamin B6. A high-yield summary section adds pKa values, reaction positions and biological roles.
Topic 37 of 42 in the MU Sofia syllabus for Chemistry (Medicine, Year 1). The free AceMed note covers it in 13 sections, about 812 words (6 min of reading), with 23 flashcards.
In this note
Heterocyclic Compounds: The Building Blocks of Life
Pyridine. Structure and acid-base properties.
Electrophilic substitution reactions (bromination and nitration).
Nucleophilic substitution reactions (reaction with sodium amide).
N-Alkylation (reaction with iodomethane).
Nicotinamide (vitamin B3), nicotinamide adenine dinucleotide and vitamin B6 - structure and biological significance.
Vitamin B3
Nicotinamide Adenine Dinucleotide (NAD):
Nicotine
High Yield
Pyridine – Structure & Properties
Reactions of Pyridine
Biological Significance
Heterocyclic Compounds: The Building Blocks of Life
Heterocyclic compounds are ring-shaped molecules where at least one atom in the ring is an element other than carbon. These "heteroatoms" are most commonly nitrogen (N), oxygen (O), or sulfur (S).
From a biological perspective, nitrogen-containing heterocycles are superstars! Some important examples include:
Pyrimidine (not Pyron)
Furan
Thiophene
Pyridine. Structure and acid-base properties.
Structure: Pyridine is a basic heterocyclic organic compound with the chemical formula C 5H 5N.
Before we talk about the Aromaticity of Pyridine we need to know the following terms :
Cyclic: The molecule has a ring structure formed by covalent bonds.
p² Hybridization: The participating carbon atoms are likely sp² hybridized, meaning they have three planar sigma bonds and one unhybridized p orbital for pi bonding. Pyridine is Cyclic as its sp2 hybridized.
Conjugation: The p orbitals of the carbon atoms overlap, allowing for delocalization of pi electrons across the ring. This delocalization is symbolized by the squiggly line (~) between carbon atoms (C-C). Pyridine is conjugated .
Hückel's Rule (4n + 2 π electrons): The number of pi electrons in the ring must follow this rule for aromaticity. In your example, 4n + 2 = 6, which suggests there are 2 pi electrons (n = 1).
Acid Base properties: Pyridine is a weak base, cannot accept proton readily because the lone pair of electron is present on sp2 hybridised 'N' and due to the more % of s-character (sp>sp2>sp3) lone pair of electrons are tightly held by the nucleus, less available for donation, therefore a weak base.
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