A systematic organic name is built from a stem that counts the carbons (meth-, eth-, prop-, but-) and an ending that names the functional group (-ol for alcohol, -oic acid for carboxylic acid, -yl…-ate for ester). Reading the name therefore tells you the chain length and the group, which a common name such as “wood alcohol” or “spirits of vinegar” does not. Record the systematic name beside the common one on every label and in every batch book.
Part of Organic Chemistry
The systematic scheme that turns a structure into an unambiguous name and back, with the common names it replaces.
The Name Carries The Structure
Two pieces make most names.
The stem counts carbons in the main chain: one carbon is meth-, two eth-, three prop-, four but-, five pent-, six hex-. The first four are historical and have to be memorised; the rest are Greek numerals.
The ending names the group: -ane for a chain with single bonds only, -ene for a double bond, -yne for a triple bond, -ol for a hydroxyl, -oic acid for a carboxyl, and -yl followed by -oate (or -ate) for an ester.
Put them together and the corpus’s own compounds read cleanly. Ethane is two carbons, single bonds. Ethanol is two carbons plus a hydroxyl. Ethanoic acid (acetic acid, the carrier’s vinegar compound) is two carbons plus a carboxyl. Ethyl ethanoate (ethyl acetate) is the ester of ethanol and ethanoic acid, named as the alcohol part first and the acid part second.
Why Common Names Are A Safety Problem
“Wood alcohol” is methanol and “grain alcohol” is ethanol, and the two are not interchangeable: methanol is the one that causes permanent blindness, as set out on the Methanol Hazards page. A container labelled only “alcohol” has no reliable meaning. “Spirits of vinegar”, “carbolic acid” (phenol) and “oil of vitriol” (sulfuric acid, an inorganic compound) are old trade names that hide whether a substance is food-safe or corrosive.
Method: Naming A Simple Compound
Step 1: Find the longest carbon chain that contains the functional group.
Step 2: Take the stem for its length.
Step 3: Add the ending for the group; for a single-bond chain with a hydroxyl, that is -ane with the final e dropped and -ol added.
Step 4: Number a side group from the end nearest the group, if any, and put its number in front.
Worked Example: From Name To Formula
Take “propan-2-ol”, the rubbing-alcohol compound. Prop- means three carbons. -an- means single bonds. -ol means a hydroxyl. The 2 says it sits on the middle carbon. Count hydrogens: the two end carbons take 3 hydrogens each (6), the middle carbon takes 1 (it has two carbon bonds and one oxygen bond, leaving one), and the hydroxyl adds 1. Total 6 + 1 + 1 = 8, so C3H8O. The same formula describes propan-1-ol, where the hydroxyl is on an end carbon, so the number is not decoration; it separates two isomers (see Isomers).
Common Mistakes
- Writing only a formula on a label. Isomers share formulas. Write the name.
- Trusting a common name from a pre-collapse bottle without checking it against a property test.
- Ignoring the ending. Names ending -ine, such as quinine, caffeine and morphine in the carrier’s alkaloid list, usually mark a nitrogen base, and several of those are poisonous.
Safety
A wrong name on a label can poison someone
Label every container with the systematic name, the hazard (flammable, corrosive, toxic) and the date. Never reuse a food or drink container. Methanol-bearing liquids in particular must read as poison; see Methanol Hazards.
What’s Next
- Learn next: Distillation Apparatus — the first practical operation in the organic workshop
- Combine with: Functional Groups — the groups the endings refer to