✍ Scribed by Ridley, Damon D.
No coin nor oath required. For personal study only.
Explore Substances searches the substance database REGISTRY, which includes all types of chemical substances such as organic, inorganic, alloys, polymers, mixtures, reactive intermediates, proteins, nucleic acids, and so forth. In most cases, the registration of substances follows exactly the valence bond descriptions taught in chemistry courses. However, the many subtle variations in structures often require modification of valence bond descriptions and the key issues are resonance, tautomerism, π -complexes, σ -complexes, radicals, and other reactive intermediates. Specific rules are applied when structures with these variations are entered into computer databases.
Computer databases also need to have rules for defining, among other things, salts, mixtures, hydrates, polymers, and alloys in which valence bond descriptions do not necessarily apply. Many of these are addressed by registering the substance as one made up of a number of components. About 10% of substances in REGISTRY are multicomponent substances, and the key is to recognize that each component is identified as a single entry in the formula and in the structure fields.
A good way to learn about the registration of substances is to examine actual records and this appendix gives examples. If further information is required it is suggested that users retrieve the substances in this appendix in SciFinder (e.g. by entering the CAS Registry Numbers of the substances in Explore Substances: Substance Identifier).
A4.1 Single-Component Substances
The most common class is that of single substances; typical records are shown for cortisone (Figure A4.1) and epibatidine (Figure A4.2) 1 .
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