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The Graphic Representation of Chemical Formulae in the Publications of International Nonproprietary Names (INN) for Pharmaceutical Substances
(1995; 53 pages) View the PDF document
Table of Contents
View the documentAcknowledgements
View the document1. INTRODUCTION
View the document2. ACYCLIC STRUCTURES
View the document3. CYCLIC STRUCTURES
View the document4. IONIC STRUCTURES
View the document5. ISOTOPICALLY MODIFIED COMPOUNDS
View the document6. COORDINATION COMPOUNDS
View the document7. STEREOCHEMISTRY
View the document8. CARBOHYDRATES
View the document9. STEROIDS
View the document10. TERPENOIDS
View the document11. PROSTANOIDS
View the document12. ALKALOIDS
View the document13. ANTIBIOTICS
View the document14. POLYPEPTIDES
View the document15. POLYMERS
View the documentAcknowledgements
View the documentReferences
 

4. IONIC STRUCTURES

4.1 In general, in ionic structures, the cationic part is placed on the left and the anionic part on the right.

4.2 Ionic charges are not encircled and are shown as superscripts on the right of the charged atom. Multiple charges are indicated by writing n+ or n- and not by writing the + or - symbol n times.

4.3 A terminal charge is shown as a superscript on the right of the group concerned, unless the order of atomic symbols in the group is reversed, when the charge is shown as a superscript on the left. In a lateral acyclic chain, if there is no space for a superscript on the right of the atom concerned, the charge can be shown immediately above that atom. When a ring is involved, the charge is usually placed outside the ring. When it is difficult to place the charge without ambiguity, it may be shown inside the ring:

4.4 In structures with delocalized charge, the structure is put in square brackets, with the charge sign outside them as a superscript on the right:

4.5 Metal salts of inorganic acids are shown without charges or bonds. If they include several metals, the symbols for the metals are shown in alphabetical order. In acid salts, the metal precedes the hydrogen. Molecules of water of crystallization or of substances of solvation follow the formula of the salt, from which they are separated by a comma:

NaBr

NaHCO3

AlK(SO4)2,12H2O

NaH2PO4,2H2O

AlCl3,4C2H5OH

For inorganic compounds, centred dots are recommended by the International Union of Pure and Applied Chemistry (2). However, several pharmacopoeias have for a long time been using the comma for both organic and inorganic compounds.

4.6 In the metal salts of organic acids and the metal compounds of alcohols, phenols (and their sulfur, selenium and tellurium analogues), amines and amides, the metal symbol usually replaces the “acid” hydrogen, but neither charges nor bonds are shown:

Nevertheless, ionic forms may be used when substances contain several “acid” groups to which the various cations cannot easily be attributed:

4.7 Amine salts are shown with the structure of the amine on the left and, after a comma, the formula of the acid on the right:

4.8 Quaternary ammonium salts and other compounds with a positive charge on a heteroatom (P, As, Sb, O, S, Se, Te) are shown in ionic form (with + and - charges), the two ions being separated by a space:

4.9 In inner salts, the positive and negative charges are shown and are normally placed in the structure as recommended above:

 

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