Main page BASIC ORGANIC NOMENCLATURE
 
The official names of organic compounds are build of four parts:

Prefix--Locant--Parent--Suffix

The prefix describes what the substituents are, and where are they located. The locant indicate the position of the the primary functional group. The parent names the longest carbon chain in the compound. The suffix describes what family the compounds belongs to. i.e. what is the primary functional group. The nomenclature rules for alkanes (i.e. compounds containing only carbon and hydrogen atoms connected by single bonds) are illustrated below. If you want to check the full names of these compounds put  the cursor above the structure.

Step 1. Find the longest continuous hydrocarbon chain and use its name as the parent name (for parent names see table below).

3-methylhexane

4-ethyl-3-methylheptane

6-carbon chain - parent: hexane

7-carbon chain - parent: heptane

The longest chain may not always be apparent from the manner of writing. If two different chains of equal length are present, chose one with the larger number of branch points as the parent. 

3-ethyl-2-methylhexane

incorrect name: 3-isopropylhexane

correct: 6-carbon chain - parent: hexane with two substituents

incorrect: 6-carbon chain - parent: hexane with one substituent

Step 2. Number the atoms in the main chain, beginning at the end nearer to the first branch point.

4-ethyl-3-methylheptane

incorrect: 4-ethyl-5-methylheptane

correct: parent heptane with the
first branch at carbon 3

incorrect: parent heptane with the
first branch at carbon 4

If there is branching an equal distance away from both ends of the parent chain, begin numbering at the end nearer to the second branch point.

3-ethyl-4,7-dimethylnonane

incorrect: 7-ethyl-3,6-dimethylnonane

correct: parent nonane with 
branches at carbons 3 and 4

incorrect: parent nonane with 
branches at carbons 3 and 6

Step 3. Identify and number the substituents (for substituent names see table below).

3-ethyl-4,7-dimethylnonane

4-ethyl-2,4-dimethylhexane

parent nonane, with substituents
ethyl on C3
methyl on C4
methyl on C7

parent hexane with substituents
methyl on C2
methyl on C4
ethyl on C4

Assign a number to each substituent, according to its point of attachment to the main chain.  If there are two substituents on the same carbon give them both the same number. There must be as many numbers in the name as there are substituents.

Step 4.  Write the name as a single word. Use hyphens to separate the different prefixes, and use comas to separate numbers. If two or more substituents are present, list them in alphabetical order. If two or more identical substituents are present, use one of the multiplier prefixes (di-, tri-, tetra-), but do not use prefixes for alphabetizing purposes.

3-methylhexane

3-ethyl-2-methylhexane

3-methylhexane

3-ethyl-2-methylhexane 

4-ethyl-3-methylheptane

3-ethyl-4,7-dimethylnonane

4-ethyl-3-methylheptane

3-ethyl-4,7-dimethylnonane

4-ethyl-2,4-dimethylhexane

4-ethyl-3,5-dimethylheptane

4-ethyl-2,4-dimethylhexane

 try this one on your own

There are more complicated cases where substituents have to be named using the same rules. These details can be found in the textbook or Nomenclature booklet.  

Here is a table of useful names for parents and substituents:

 

No of carbons parent name parent alkane substituent name
1 meth methane methyl
2 eth ethane ethyl
3 prop propane propyl
4 but butane butyl
5 pent pentane pentyl
6 hex hexane hexyl
7 hept heptane heptyl
8 oct octane octyl
9 non nonane nonyl
10 dec decane decyl

Organic compounds containing other functional groups are named based on the same principles, with each group having its characteristic name.  A very small selection of these names is shown in a table below, together with some commonly used names. 

 

Functional group Group suffix Example Common name
alkenes -ene ethene ethylene
alkynes -yne ethyne acetylene
alcohols -ol 
(replacing "e" in alkane name)
ethanol ethyl alcohol
ethers (alkyl alkyl) ether
(alkyl names as in substituent names)
diethyl ether ether
amines -amine
(added to the substituent name)
dimethylamine --
aldehydes -al
(replacing "e" in alkane name)
methanal formaldehyde
ketones -one
(replacing "e" in alkane name)
2-propanone acetone
carboxylic acids -oic acid
(replacing "e" in alkane name)
ethanoic acid acetic acid
esters alkyl -ate
(where "ate" replaces "oic" in the acid name)
ethyl ethanate ethyl acetate
amides amide
(where "amide" replaces "oic" in the acid name)
hexanamide --

 

Tutorials Last updated 08/07/12 Copyright 1997-2013
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