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Organic Chemistry: Compound Identification Tips

Name That Compound

There are different ways your substance is identified in chemical literature, some are more precise than others. All of these below are for the same substance.

CAS Registry Number Molecular Formula Substance Name(s) Chemical Structure
103-90-2 C8 H9 N O2 Acetamide, N-​(4-​hydroxyphenyl)​-
Acetanilide, 4'-hydroxy-
4-(Acetylamino)phenol
p-Hydroxyacetanilide
Acetaminophen
Panadol
Paracetamol
Tylenol

CAS Registry Numbers?

CAS Registry Numbers are unique identifiers assigned to substances by Chemical Abstracts Service and maintained in their CAS Registry. You can search these SciFinder, as well as numerous online and print sources to find your chemical.

There are now more than 156 million substances in the Registry, with about 15,000 new substances are added daily. Each CAS RN is made up of three sets of numbers divided by hyphens.

50-00-0 - Formaldehyde (lowest assigned number)

58-08-2 - Caffeine

2101814-41-7 (added in 2017)

Molecular Formula

Molecular formulas are often written using the Hill System. Some databases like Reaxys also use this system (NaCl becomes ClNa), as well as print handbooks.

Start with carbon, then hydrogen, then the rest of the in alphabetical order (C2H5AlCl2). If there's no carbon, write all of the elements in alphabetical order (ClHN4)

The challenge with searching molecular formulas is that many substances can have the same molecular formula, like C8H8O3, the molecular formula for vanillin, methyl salicylate, p-anisic acid, methylparaben, mandelic acid, phenoxyacetic acid, and more.

Substance Names

You can always search for chemical information by searching on the substance name itself.

Spelling matters. If you get zero hits, check the spelling first.

Databases will usually include alternate names, but often do not list all of them. You may need to search for more than one name, and if that doesn't work try the CAS-RN.

There may be spelling and word order variations to watch for. You might see "chloro-benzoic" or "chlorobenzoic," "methyl 2-hydroxybenzoate" or "2-hydroxymethylbenzoate," or "2-bromo-5-methyl-pyridine" or "2-bromo-5-methylpyridine."

Structure

Most databases have a structure editor where you can draw or import a structure. There may also be reaction and substructure searching available. As with getting zero hits in a name search, if you get zero hits on a structure search make sure you drew it correctly.

SciFinder and Reaxys are now integrated into ChemDraw, so you can launch and search the databases while in ChemDraw.

Each editor has its own quirks and steps for things like adding functional groups and R-groups, reaction roles, charges, etc. Consult the help menu if you have questions.