Heterocyclic compounds contain rings with at least two different elements, with one usually being carbon. They can be classified based on ring size, with common 5-membered rings including furan, thiophene, and pyrrole, and common 6-membered rings including pyridine and pyran. Many heterocycles like pyrrole are aromatic due to resonance stabilization. Rings are involved in various reactions like electrophilic substitution and oxidation.

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3. Heterocyclic
Ring
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4.  A heterocyclic compound is a cyclic
compound that has atoms of at least two
different elements as members of its ring(s).
The counterparts of heterocyclic compounds
are homocyclic compounds, the rings of
which are made of a single element.
 Although heterocyclic compounds may be
inorganic, most contain at least one carbon
atom, and one or more atoms of elements
other than carbon within the ring structure,
such as sulfur, oxygen, or nitrogen.
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5.  Classification based on electronic structure
 5-Membered rings
 6-Membered rings
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6.  5-Membered rings
i.e – Furan, Thiphene, Pyrrole
 6-Membered rings
i.e – Pyridine, Pyran
 Benzofused rign
 i.e – Indole ring, Quinoline ring etc
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7.  With heterocycles containing five atoms, the
unsaturated compounds are frequently more stable
because of aromaticity.
i.e - Puran,, Pyrrole,Thiphene etc
 Puran, It is an aromatic compound.
Because it has Resonance structure.
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8. Pyrrole ring
It is also a aromatic compound.
It show aromaticity in its structure.
Synthesis of Pyrrole:
Pyrrole can be synthesized from
 mucic acid
 Acetylene
 Paal-knorr synthesis
 Succinamide
 Furan etc
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9.  Pyrole ring is acidic.
 Pyrrol donate proton in reaction for this
reason,it is acidic in nature.
 Chemical Reaction of Pyrrole .
 It gives Electrophilic substitution reaction
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10.  Six-membered rings with a single heteroatom
i.e – Pyridine
 Synthesis of pyridine:
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11.  Chemical reaction of Pyridine
 -Electrophilic Substitution reaction of
pyridine.
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12.  Benzofuse ring such as Indole ring, Quinoline
ring, Isoquinoline ring.
 Indole synthesis
 Leigngruber-Batcho indole synthesis
 Fisher indole synthesis
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13.  Electrophilic Substitution reaction
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14.  Oxidation of indole
 Due to the electron-rich nature of indole, it
is easily oxidized. Simple oxidants such as N-
bromosuccinimide will selectively oxidize
indole 1 to oxindole (4 and 5).
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16.  Halogenation reaction of Isoquinoline
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