The Basics
Organic chemistry names follow IUPAC (International Union of Pure and Applied Chemistry) rules. Most names are built from up to four parts:
- Locants / substituent prefixes — numbers and names of branches or attached groups (e.g. 2-methyl-, 3-chloro-).
- Root prefix — how many carbon atoms are in the main chain (e.g. meth-, eth-, prop-).
- Infix — position of unsaturation or ring (e.g. but-2-en-).
- Suffix — the principal functional group (e.g. -ane, -ol, -oic acid).
Example: 3-methylbut-1-ene = 3-methyl (branch on carbon 3) + but (4 carbons) + 1-ene (double bond starting at carbon 1).
Carbon-Count Prefixes
These prefixes tell you how many carbons are in the main chain, regardless of functional group.
| Carbons | Prefix | Example (alkane) |
|---|---|---|
| 1 | meth- | methane |
| 2 | eth- | ethane |
| 3 | prop- | propane |
| 4 | but- | butane |
| 5 | pent- | pentane |
| 6 | hex- | hexane |
| 7 | hept- | heptane |
| 8 | oct- | octane |
| 9 | non- | nonane |
| 10 | dec- | decane |
Substituent (-yl) Groups
When a carbon chain branches off the main chain, it becomes a substituent named with -yl instead of -ane.
| Group | Formula | From |
|---|---|---|
| methyl | –CH3 | methane |
| ethyl | –CH2CH3 | ethane |
| propyl | –CH2CH2CH3 | propane |
| isopropyl | –CH(CH3)2 | propane (branched) |
| butyl | –CH2CH2CH2CH3 | butane |
| tert-butyl | –C(CH3)3 | butane (branched) |
| vinyl (ethenyl) | –CH=CH2 | ethene |
| phenyl | –C6H5 | benzene |
Example: 2-methylpropane has a methyl branch on carbon 2 of a propane chain.
Suffixes & Functional Groups
| Suffix / Prefix | Functional Group | Example |
|---|---|---|
| -ane | all single bonds (saturated) | propane |
| -ene | C=C double bond | but-2-ene |
| -yne | C≡C triple bond | but-1-yne |
| -ol | alcohol, –OH | propan-1-ol |
| -al | aldehyde, –CHO | propanal |
| -one | ketone, C=O mid-chain | propan-2-one (acetone) |
| -oic acid | carboxylic acid, –COOH | propanoic acid |
| -oate | ester, –COO– | methyl propanoate |
| -amine | amine, –NH2 | propan-1-amine |
| -amide | amide, –CONH2 | propanamide |
| -nitrile | nitrile, –C≡N | propanenitrile |
| fluoro- | –F substituent | 1-fluoropropane |
| chloro- | –Cl substituent | 1-chloropropane |
| bromo- | –Br substituent | 1-bromopropane |
| iodo- | –I substituent | 1-iodopropane |
| alkoxy- (e.g. methoxy-) | ether, –O–R | 1-methoxypropane |
Numbers (locants) show where the feature sits on the chain — counted to give the lowest possible number to the principal group. but-1-ene and but-2-ene are different molecules: the double bond starts at carbon 1 or carbon 2.
Straight-Chain Alkanes (CnH2n+2)
| Name | Formula | Carbons |
|---|
Biological Molecules
Many molecules central to biology follow the same naming logic, though common names are often used instead.
| Molecule | Category | Formula | Note |
|---|
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