Nomenclature of Hydrocarbon chain Aliphatic Compunds
(Alkanes, Alkenes & Alkynes)
Aromatic Compounds


Hydrocarbons are the simplest organic compounds . Containing only carbon and hydrogen, they can be straight-chain, branched chain, or cyclic molecules.

Carbon tends to form four bonds in a tetrahedral geometry. Hydrocarbon derivatives are formed when there is a substitution of a functional group at one or more of these positions.

There are three types of homologous families of hydrocarbons: alkanes, alkenes and alkynes. Alkanes contain only single bonds between carbon atoms. Alkenes contain at least one double bond. Alkynes contain at least one triple bond. Most of these types of hydrocarbons can exist with the same chemical formula in different form or chemical structure. When a compound has the same chemical formula but two possible structures, these two structures are called isomers.

Derivatives of Hydrocarbons

An almost unlimited number of carbon compounds can be formed by the addition of a functional group to a hydrocarbon.


Nomenclature of Hydrocarbon Chain

The IUPAC, or International Union of Pure and Applied Chemistry, method is the currently accepted method for naming hydrocarbon chains.

The steps are as follow::

1. Locate the longest continuous chain of carbon atoms. Remember that the longest chain may be bent.

2. Number your chain from the end nearest a double or triple bond, otherwise from the end with the closest branch.

3. Use Greek numerical prefixes to find the "parent name" of your compound. This is based on the size of your longest chain. For example, if you have a C6 (6-carbon chain) molecule, it is considered a hexane. C7 is heptane, C8 is octane, and so on. These are all alkanes (single bonds only).

o Alkenes: If the chain contains a double bond end the name with -ene. For example, a C9 containing a double bond is a nonene. Place the number of the adjacent carbon in front of the name.
Ex: CH2=CHCH2CH3is 1-butene.

o Alkynes: If the chain contains a triple bond end the name with -yne. For example a C5 containing a triple bond is a pentyne.

o Multiple double bonds take the form -diene, -triene, etc., with the size prefix of the chain taking an extra "a". Alkynes are named using the same system, with the suffix "-yne" indicating a triple bond. Ex: CH2=CHCH=CH2 is 1,3-butadiene.

o Prefixes:
1: methyl
2: eth
3: prop
4: but
5: pent
6: hex
7: hept
8: oct
9: non
10: dec

4. Name your side chains. They are named for the carbon on the main chain to which they are attached. For example, if you have a C1 compound attached to the second carbon in the chain, it is called a 1-ethyl group (use the same prefixes as above). If there is more than one of the same group , add the number of the carbon of attachment to the name. Using the previous example with the addition of a methane on the the third carbon as well, you would name it a 1,3-dimethyl group.

Prefixes for groups:
o 2: di
o 3: tri
o 4: tetra

5. Arrange your side chains in alphabetical order and tack them on before your parent name. Complex side chains go in parentheses.

6. Keep practicing! Before you know it, you'll be able to name or draw a 1,2-di(1,2 dimethyl ethyl) cyclopentane with ease!


Aliphatic Compounds


Alkanes are saturated hydrocarbons since they only have single covalent bonds. Examples of Alkanes, are the gases produced by fractional distilation.
Alkanes have the general formula of CnH2n+2, below is a table of the first four alkanes in increasing order of carbon atoms.


Alkenes are unsaturated since they have a double covalent carbon bond. Alkenes have the general formula CnH2n.


Alkynes (acetylenes) are unsaturated necyclical hydrocarbons which contain one or more triple bonds between atoms of carbon. The general formula for alkynes is CnH2n-2


Aromatic Compounds

Aromatic compounds derive their names from the fact that many of these compounds in the early days of discovery were grouped because they were oils with fragrant odours, hence the name aromatic.

The current definition of aromatic compounds includes only those with a benzene ring, which is a special six carbon ring compound with three alternating double bonds. This structure imparts unique properties to benzene which are different from other ring compounds.


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