WELCOME M.Sc. II S.M. Joshi College By Prof. Pawar A. A.

HETEROCYCLIC COMPOUNDS

DEFINITION OF HETEROCYCLIC COMPOUNDS: Heterocyclic compounds are cyclic compounds which contains one/more atoms of other elements along with carbon atoms. DEFINITION OF HETEROATOM: Hetero atoms are those which contains an atom other than carbon such as nitrogen, sulphur, phosphorus etc.

CLASSIFICATION: Depending upon the size of heterocyclic ring, they are classified into diferent types. Five membered heterocyclic compounds: Six membered heterocyclic compounds:

Fused heterocyclic compounds:

Condensed ring systems: NOMENCLATURE Systematic nomenclature system is used for naming 3-10 membered monocyclic heterocyclics of various degree of the unstauration containing one/more heteroatoms. It specifies the following characters such as: - the ring size -the nature -the type of heteroatom - the position of heteroatom etc.

These hetrocompounds are also comply with the general rule that is proposed by the “Huckel Rule ” “Huckel rule” states that aromaticity is obtained in the cyclic conjugated and planer system containing (4n+2) π electrons. The heterocyclic compounds are named by fusing the following rules: -Combination of prefixes with stem -The prefixes for different heteroatoms.

Prefixes for different Heteroatoms S.No: Heteroatom Symbol Valence Prefix 1 Oxygen o 2 oxa Sulphur s Thia 3 Nitrogen N Aza 4 Phosphorus P Phospha

If the heteroatoms are different they are named in the order of “O, S, N, P, Si” etc. by combining the prefixes with the ending in the order of preference. Eg: -The state of hydrogenation is indicated in the suffix or by the prefixes dihydro, tetrahydro etc or by prefixing the name of the parent unsaturated compound with the symbol ”H” preceeded by a number indicating the position of saturation. Eg:

In a monocyclic compound containing only one heteroatom numbering starts at this atom. The ring is numbered to give the substituents or other heteroatoms the lowest number possible. Eg: NOMENCLATURE OF FUSED HETEROCYCLIC COMPOUNDS: . When the parent compound has been choosen, its name is prefixed by the name of the fused ring attached (ex: benz (0),napth(o)) also the parent compound choosen is the component containing the largest number of rings and has a simple name. Eg:

. Numbering is then carried out in a clockwise direction starting with the uppermost ring farthest to right and omitting atoms at right junctions. Ex -In a heterocyclic ring numbering preferably commence at a saturated rather than at an unsaturated heteroatom

Bicyclic bridged structures are quite common Bicyclic bridged structures are quite common. The nomenclature of such a structure consists of the prefix bicycle, followed in square brackets the number of carbon atoms separating the bridge heads by the three possible routes in descending numerical order. Eg:

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