14.3 Heterocyclic compounds with two nitrogen atoms.
Covers imidazole (1,3-diazole): its five-membered ring with two nitrogens, aromatic character, and amphoteric behaviour with one nitrogen acting as an acid and the other not basic. It then explains tautomerism in imidazole, linking it to histidine and histamine, including histamine's effects and synthesis, and antihistamines (H-1 and H-2 blockers). Pyrimidine (1,3-diazine) follows, with its weak basicity and substitution sites, then N-alkylation, pyrimidine bases cytosine, uracil and thymine, and purine with adenine and guanine. The note ends with caffeine as a xanthine-derived purine.
Topic 38 of 42 in the MU Sofia syllabus for Chemistry (Dental Medicine, Year 1). The free AceMed note covers it in 8 sections, about 759 words (5 min of reading), with 23 flashcards.
In this note
Heterocyclic compounds with two nitrogen atoms. (1,3-diazole). Structure.
acid-base properties
Tautomerism in imidazole derivatives. Histidine and histamine.
Antihistamines.
Pyrimidine (1,3-diazine).
N-Alkylation (reaction with iodomethane).
Pyrimidine bases: cytosine, uracil and thymine.
Caffeine.
Heterocyclic compounds with two nitrogen atoms. (1,3-diazole). Structure.
Structure:
Imidazole is a five-membered heterocyclic compound, also known as 1,3-diazole.
It contains two nitrogen atoms and three carbon atoms in a ring structure.
Properties:
Aromatic: Imidazole exhibits aromatic character due to its cyclic structure and electron delocalization.
Amphoteric: Imidazole can act as both an acid (H+ donor) and a base (H+ acceptor) due to the presence of two nitrogens with different properties.
One nitrogen atom (N1) can donate a proton (acidic).
The other nitrogen atom (N2) lacks a lone pair and cannot accept a proton (not basic).
Reactions:
Imidazole can undergo substitution reactions (SN2 mechanism) at positions 4 and 5 of the ring.
Tautomerism in imidazole derivatives. Histidine and histamine.
Tautomerism: Imagine a molecule that can exist in two very similar forms, like a shape-shifter. These forms, called tautomers, share the same atoms but have a flipped proton and its electron pair within the molecule.
Imidazole: This five-membered ring with two nitrogens is particularly good at this shape-shifting due to the presence of a lone pair on one nitrogen.
The Flip: The lone pair can attract a proton from the other nitrogen, creating two possible forms:
N-H Tautomer: Proton sits on a specific nitrogen (N).
N+ Tautomer: Proton is on the other nitrogen, with a positive charge (N+).
Fast Change: These forms are constantly switching back and forth, making it difficult to isolate one form.
Why It Matters: Tautomerism affects the reactivity of imidazole derivatives and plays a role in the function of biomolecules like histidine.
Histidine:
Amino Acid: Histidine is an essential amino acid, meaning your body can't produce it and needs to obtain it from food.
Structure: It has a unique structure with an imidazole ring (a five-membered ring containing two nitrogens) attached to its central carbon backbone.
Histamine:
Biogenic Amine: Histamine is a signaling molecule with various functions in the body.
Neurotransmitter: It acts as a neurotransmitter in the brain, involved in sleep-wake regulation, learning, and memory.
Immune Response: Histamine also plays a crucial role in the immune response, especially allergic reactions. It triggers inflammation, itching, and mucus production when released by immune cells.
Symptoms: When released excessively during allergic reactions, histamine can cause:
Diarrhea
Headache
Asthma
Hypotension (low blood pressure)
Treatment: These symptoms can be alleviated by antihistamines, medications that block histamine receptors.
Synthesis: Histamine is formed by a simple process called decarboxylation, where a carboxyl group (COOH) is removed from histidine by an enzyme.
The Connection:
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