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warning But First, a word about:
Why Chemical Names can be trouble...



The conventions for naming organic compounds are very complex and difficult to understand. A given molecule might have dozens of different names, depending on who's naming it and what search tool you're using. Generic or trivial names, acronyms, trade names, and any number of systematic names such as IUPAC-style names, may be used throughout the literature.

As a general rule, it's best to avoid using a chemical name as a search term unless the name is almost universally recognized and widely used. You're probably OK with names like toluene and ammonia. But even toluene has a synonym (methylbenzene) that describes its structure more accurately. The more complex the structure gets, the more names it can have and the more likely you are to miss something.

Further, using a chemical name as a simple keyword will not only retrieve (possibly) the compound you're actually looking for, but also any compound that contains that name within a larger name string, potentially leading you far astray.

So what to do?

Most databases and handbooks have substance indexing by molecular formula. The formula for toluene is C7H8. Formulas get around the name problem to an extent, but they are also ambiguous, and you still will have to choose from a list of matching names.

Fortunately, Chemical Abstracts Service (CAS) provides a great alternative to names and formulas with the CAS Registry Number, which serves as an unambiguous search term in many kinds of scientific databases. Use the RN if you have it, and if you don't have it it's a good idea to find it first.

Ultimately, the Registry Number is a shortcut to the chemical structure. The structure is the only unambiguous way to describe a molecule. Many databases allow you to draw a structure and search it. This can be a little tedious, but if there's any doubt you should do so. Toluene looks like this:

toluene
Toluene's Registry Number is 108-88-3. For more information see our page on finding and using Registry Numbers.

Other identifiers that serve a useful function similar to RNs (i.e. avoiding using a name) include InChI and SMILES structure notations. Unlike RNs, which carry no chemical meaning in themselves, InChI and SMILES are textual encodings of a chemical structure that can be generated and read without reference to a proprietary database. These are newer protocols and not as widely recognized as RNs, but many web-based chemical databases use them as interconnecting shortcuts.

Now, on to the show...


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