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Sub-Chapter X ORGANO-INORGANIC COMPOUNDS, HETEROCYCLIC COMPOUNDS, NUCLEIC ACIDS AND THEIR SALTS, AND SULPHONAMIDES
GENERAL
The organo-inorganic compounds covered by headings 29.30 and 29.31 are organic compounds whose molecules contain, in addition to atoms of hydrogen, oxygen or nitrogen, those of metals or other non-metals (such as sulphur, arsenic, lead, iron, etc.) directly linked to carbon.
Heading 29.30 (organo-sulphur compounds) and heading 29.31 (other organo-inorganic compounds) do not include sulphonated or halogenated derivatives (including compound derivatives) which, apart from hydrogen, oxygen and nitrogen, only have directly linked to carbon the atoms of sulphur or of halogens which give them their nature of sulphonated or halogenated derivatives (or compound derivatives).
Headings 29.32 to 29.34 cover heterocyclic compounds.
The term "heterocyclic" refers to organic compounds composed of one or more rings, and which contain in the ring(s), in addition to the carbon atoms, atoms of other elements such as oxygen, nitrogen or sulphur. In this way, the following heterocyclic groups are derived : (A) FIVE-MEMBERED RINGS (1) Containing one hetero-atom : (a) Of oxygen : Furan group (heading 29.32)*. (b) Of sulphur : Thiophen group (heading 29.34)*. (c) Of nitrogen : Pyrrole group (heading 29.33)*. (2) Containing two hetero-atoms : (a) One oxygen, one nitrogen : Oxazole and isoxazole groups (heading 29.34)*. (b) One sulphur, one nitrogen : Thiazole group (heading 29.34)*. (c) Two nitrogen : Imidazole and pyrazole groups (heading 29.33)*. (3) Containing three or more hetero-atoms : (a) One oxygen, two nitrogen : Furazan group (heading 29.34)*. (b) Three nitrogen : Triazole group (heading 29.33)*. (c) Four nitrogen : Tetrazole group (heading 29.33)*. (B) SIX-MEMBERED RINGS (1) Containing one hetero-atom : (a) Of oxygen : Pyran group (heading 29.32)*. (b) Of sulphur : Thiin (Thiapyran) group (heading 29.34)*. (c) Of nitrogen : Pyridine group (heading 29.33)*. (2) Containing two hetero-atoms : (a) One oxygen, one nitrogen : Oxazine group (heading 29.34)*. (b) One sulphur, one nitrogen : Thiazine group (heading 29.34)*. (c) Two nitrogen : Pyridazine, pyrimidine, pyrazine and piperazine groups (heading 29.33)*. (C) OTHER MORE COMPLEX HETEROCYCLIC COMPOUNDS
These result from the condensation of five- or six-membered heterocyclic compounds with other carbocyclic rings.
Examples include the following groups : (a) Coumarone (heading 29.32)*. (b) Benzopyran (heading 29.32)*. (c) Xanthene (heading 29.32)*. (d) Indole (heading 29.33)*. (e) Quinoline and isoquinoline (heading 29.33)*. (f) Acridine (heading 29.33)*. (g) Benzothiophene (Thionaphthene) (heading 29.34)*. (h) Indazole (heading 29.33)*. (ij) Benzimidazole (heading 29.33)*. (k) Phenazine (heading 29.33)*. (l) Phenoxazine (heading 29.34)*. (m) Benzoxazole (heading 29.34)*. (n) Carbazole (heading 29.33)*. (o) Quinazoline (heading 29.33)*. (p) Benzothiazole (heading 29.34)*. For the purposes of headings 29.32 to 29.34, with respect to compounds containing more than one heterocyclic ring, if only one of the heterocyclic rings is specifically named in a subheading within headings 29.32 to 29.34, the compound should be classified in that subheading. However, if two or more of the heterocyclic rings are specifically named at the subheading level, the compound should be classified in the specific subheading that occurs last in numerical order.
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