Common vs. IUPAC Names
The IUPAC system can name any organic compound unambiguously. So why do chemists still use common names like “acetone” instead of “propan-2-one”? Because common names are shorter, older, and deeply embedded in chemistry culture. Acetone has been called acetone since the 1830s. No one in a lab says “please pass the propan-2-one.” And the MCAT knows this - passages use common names constantly, especially for well-known compounds.
Your job is to know both naming systems and translate between them instantly. When a passage says “formaldehyde,” you need to see HCHO in your mind. When it says “ethanoic acid,” you need to recognize it as acetic acid (vinegar). This section gives you the definitive list of common names the MCAT expects you to know.
Why Two Systems Exist
Common names predate IUPAC naming by centuries. They came from sources (formic acid from ants), properties (glycerol from the Greek for “sweet”), or discoverers. These names carry no structural information - “acetone” tells you nothing about the three carbons or the carbonyl. But they are so widely used in biology, medicine, and industry that IUPAC officially accepts many of them as alternative names.
The Must-Know Common Names
Here is the definitive table of common names that appear on the MCAT. If you know all of these, you will never be caught off guard by a passage.
Carboxylic Acids and Derivatives
| Common Name | IUPAC Name | Formula | Notes |
|---|---|---|---|
| Formic acid | Methanoic acid | HCOOH | From ants (Latin: formica) |
| Acetic acid | Ethanoic acid | CH3COOH | Vinegar; acetate ion in biology |
| Propionic acid | Propanoic acid | CH3CH2COOH | ”First fat acid” (Greek) |
| Butyric acid | Butanoic acid | CH3(CH2)2COOH | Rancid butter smell |
| Oxalic acid | Ethanedioic acid | HOOC-COOH | Krebs cycle; kidney stones |
| Succinic acid | Butanedioic acid | HOOC(CH2)2COOH | Krebs cycle intermediate |
Aldehydes and Ketones
| Common Name | IUPAC Name | Formula | Notes |
|---|---|---|---|
| Formaldehyde | Methanal | HCHO | Preservative; smallest aldehyde |
| Acetaldehyde | Ethanal | CH3CHO | Ethanol metabolism product |
| Acetone | Propan-2-one | CH3COCH3 | Simplest ketone; common solvent |
Aromatic Compounds
| Common Name | IUPAC Name | Structure | Notes |
|---|---|---|---|
| Toluene | Methylbenzene | C6H5CH3 | Common solvent |
| Phenol | Hydroxybenzene | C6H5OH | Weak acid (pKa ~ 10) |
| Aniline | Aminobenzene | C6H5NH2 | Parent of azo dyes |
| Benzoic acid | Benzenecarboxylic acid | C6H5COOH | Common preservative |
| Benzaldehyde | Phenylmethanal | C6H5CHO | Almond smell |
| Anisole | Methoxybenzene | C6H5OCH3 | Ether of phenol |
| Styrene | Ethenylbenzene | C6H5CH=CH2 | Polystyrene monomer |
| Acetophenone | 1-phenylethan-1-one | C6H5COCH3 | Aromatic ketone |
Alcohols and Ethers
| Common Name | IUPAC Name | Formula | Notes |
|---|---|---|---|
| Methanol | Methanol | CH3OH | ”Wood alcohol”; toxic |
| Ethanol | Ethanol | CH3CH2OH | ”Grain alcohol”; in beverages |
| Isopropanol | Propan-2-ol | (CH3)2CHOH | ”Rubbing alcohol” |
| Glycerol (glycerin) | Propane-1,2,3-triol | HOCH2CH(OH)CH2OH | Backbone of triglycerides |
| Diethyl ether | Ethoxyethane | (CH3CH2)2O | Classic anesthetic |
Amines and Amides
| Common Name | IUPAC Name | Formula | Notes |
|---|---|---|---|
| Aniline | Aminobenzene | C6H5NH2 | Also listed under aromatics |
| DMF | N,N-dimethylmethanamide | HCON(CH3)2 | Polar aprotic solvent |
| Urea | Diaminomethanal (carbonyl diamide) | H2NCONH2 | Nitrogen waste product |
Patterns to Notice
Several patterns make common names easier to remember:
The “form-” root comes from formic acid (methanoic acid). Compounds with one carbon in the acyl group use “form-”: formaldehyde (methanal), formamide (methanamide), formate (methanoate).
The “acet-” root comes from acetic acid (ethanoic acid). Compounds with two carbons in the acyl group use “acet-”: acetaldehyde (ethanal), acetone (propan-2-one), acetamide (ethanamide), acetyl chloride (ethanoyl chloride).
What the MCAT Actually Tests
The MCAT uses common names in two main ways:
1. In passage context: A passage might describe “the conversion of acetaldehyde to acetate” and expect you to recognize these as a two-carbon aldehyde being oxidized to a two-carbon carboxylate. If you do not know the common names, you cannot follow the passage.
2. In answer choices: A question might ask you to identify a product and list both common and IUPAC names among the answer choices. “Acetic acid” and “ethanoic acid” are the same compound - do not pick both or neither.
The MCAT rarely asks you to convert between naming systems directly (“What is the IUPAC name for acetone?”). Instead, it uses common names within passages and expects you to understand the structure and reactivity without breaking stride.
Amino Acid Common Names
Every amino acid has a common name (glycine, alanine, valine, etc.) that you must memorize for the MCAT. These are covered in the Biochemistry book, but the naming connection is important: amino acid names are purely common names - they bear no relationship to IUPAC nomenclature. “Glycine” does not tell you about its two-carbon backbone or its amino and carboxyl groups. You simply have to memorize each structure with its name and three-letter/one-letter abbreviations.
Quick Reference: Translating Names
When you encounter an unfamiliar common name on the MCAT, use these clues to decode it:
| Clue in the Name | Likely Structure |
|---|---|
| ”-ic acid” ending | Carboxylic acid |
| ”-aldehyde” ending | Aldehyde |
| ”-one” ending | Ketone (already IUPAC) |
| “-ol” ending | Alcohol (already IUPAC) |
| “-amine” ending | Amine (already IUPAC) |
| “-ine” ending | Often an amine (aniline, histamine) |
| “form-” prefix | One-carbon acyl group |
| ”acet-” prefix | Two-carbon acyl group |