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Pyrrole is an extremely weak base for an amine, with a conjugate acid pK a of −3.8. The most thermodynamically stable pyrrolium cation (C 4 H 6 N +) is formed by protonation at the 2 position. Substitution of pyrrole with alkyl substituents provides a more basic molecule—for example, tetramethylpyrrole has a conjugate acid pK a of +3.7.
For example, with the benzo-fused unsaturated nitrogen heterocycles, pyrrole provides indole or isoindole depending on the orientation. The pyridine analog is quinoline or isoquinoline, and the class of analogues with two nitrogen atoms is known as the benzodiazines. For azepine, benzazepine is the preferred name.
Imidazole is a planar 5-membered ring, that exists in two equivalent tautomeric forms because hydrogen can be bound to one or another nitrogen atom. Imidazole is a highly polar compound, as evidenced by its electric dipole moment of 3.67 D, [12] and is highly soluble in water.
Imidazole and other five-membered aromatic heterocyclic systems with two nitrogens are extremely common in nature and form the core of many biomolecules, such as histidine. Compound classes [ edit ]
Pyrrole–imidazole polyamides (PIPs) are a class of polyamides have the ability to bind to minor grooves found in the DNA helix. [ 1 ] [ 2 ] Scientists are experimenting with it as a drug-delivery mode that can switch genes on and off, as well as epigenetic modification in gene therapy .
Several rings contain basic as well as non-basic nitrogen atoms, e.g., imidazole and purine. In the non-basic rings, the lone pair of electrons of the nitrogen atom is delocalized and contributes to the aromatic pi-electron system. In these compounds, the nitrogen atom is connected to a hydrogen atom.
Pyrrole is another compound made up of molecules with a five-membered heterocyclic ring. These molecules are unsaturated and contain a nitrogen atom in the ring. Four pyrrole rings are joined in a ring structure called a porphyrin. The rings of porphyrin are components of hemoglobin, myoglobin, vitamin B12, chlorophyll, and cytochromes.
Indole undergoes electrophilic substitution, mainly at position 3 (see diagram in right margin). Substituted indoles are structural elements of (and for some compounds, the synthetic precursors for) the tryptophan-derived tryptamine alkaloids, which includes the neurotransmitter serotonin and the hormone [ 6 ] melatonin , as well as the ...