ABSTRACT
In most print and electronic resources, including Chemical Abstracts and Reaxys®, molecular formulae are given in Hill system order. When working out the molecular formula of a neutral organic compound, it is useful to remember that there must be an even number of odd-valent atoms. Chemical Abstracts Service (CAS) registry numbers are widely used to identify chemical substances in public, commercial and regulatory chemical databases and in chemical catalogues. The registry number in itself has no chemical significance but is simply a serial number assigned as a substance is entered into registry system for the first time. Racemates having more than one chiral centre are indexed, registered and named as having only relative stereochemistry. InChI stands for IUPAC International Chemical Identifier and was developed to enable easy linking of diverse data compilations. Simplified molecular-input line-entry system (SMILES) strings may be converted back to two-dimensional structures using structure diagram generation programs, of which there are several on the market.
