Question

what is heterocyclic compounds and how are they numbered???
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Answer 1

Answer:

When naming such compounds the side of the heterocyclic ring is labeled by the letters a, b, c, etc., starting from the atom numbered 1. Therefore side 'a' being between atoms 1 and 2, side 'b' between atoms 2 and 3, and so on as shown below for pyridine.

Answer 2

Heterocyclic compounds are cyclic or aromatic ring-like compounds that do not have a uniform or symmetrical structure apart from carbon they also have another element such as sulphur, nitrogen, phosphorous or oxygen.

Examples of Heterocyclic compounds include Pyridine ( C5H5N),

Aniline ( C6H5NH2), 2-Methylpyridine ( C5H5NCH3) .

Heterocyclic molecules are always numbered from the carbon that is part of the main carbon ring which is closest to or attached to the other element or other functional group.

For an example, refer to the image attached below,

Here, Nitrogen is attached to the benzene ring, numbering is done from the nitrogen and the IUPAC name will be: 1-Bromo-5-chloropyridine