IUPAC nomenclature in Organic chemistry
Important Rules
There are some important rules that we need to follow for IUPAC naming.In order to name organic
compounds you must first memorize a few basic names. These names are listed within the discussion of
naming alkanes. In general, the base part of the name reflects the number of carbons in what you have
assigned to be the parent chain. The suffix of the name reflects the type(s) of functional group(s) present
on (or within) the parent chain. Other groups which are attached to the parent chain are called
substituents.
A.Alkanes - saturated hydrocarbons
The names of the straight chain saturated hydrocarbons for up to a 12 carbon chain are shown below.
The names of the substituents formed by the removal of one hydrogen from the end of the chain is
obtained by changing the suffix -ane to -yl.
Number of Carbons Name
1 methane
2 ethane
3 propane
4 butane
5 pentane
6 hexane
7 heptane
8 octane
9 nonane
10 decane
11 undecane
12 dodecane
Here is a simple list of rules to follow. Some examples are given at the end of the list.
Identify the longest carbon chain. This chain is called the parent chain.
, Identify all of the substituents (groups appending from the parent chain).
Number the carbons of the parent chain from the end that gives the substituents the lowest numbers.
When compairing a series of numbers, the series that is the "lowest" is the one which contains the
lowest number at the occasion of the first difference. If two or more side chains are in equivalent
positions, assign the lowest number to the one which will come first in the name.
If the same substituent occurs more than once, the location of each point on which the substituent
occurs is given. In addition, the number of times the substituent group occurs is indicated by a prefix (di,
tri, tetra, etc.).
If there are two or more different substituents they are listed in alphabetical order using the base name
(ignore the prefixes). The only prefix which is used when putting the substituents in alphabetical order is
iso as in isopropyl or isobutyl. The prefixes sec- and tert- are not used in determining alphabetical order
except when compared with each other.
If chains of equal length are competing for selection as the parent chain, then the choice goes in series
to:
a) the chain which has the greatest number of side chains.
b) the chain whose substituents have the lowest- numbers.
c) the chain having the greatest number of carbon atoms in the smaller side chain.
d)the chain having the least branched side chains.
A cyclic (ring) hydrocarbon is designated by the prefix cyclo- which appears directly in front of the base
name.
Example 1
Let's start with a simple example. To name this compound, we need to first find the longest continuous
carbon chain, which is these two carbons here.
Number the chain forward and backward.
Count the number of carbons in the chain.
Based on the number of carbons, determine the prefix for the compound name.
Determine the type of bond between the carbon atoms.
Combine the prefix and the bond type to get the IUPAC name.
In this example, the compound has two carbons, so the name will start with "eth-". Since there is a
single bond between the carbon atoms, it is an alkane, so the name will end with "-ane". Therefore, the
IUPAC name of this compound is "ethane".
Important Rules
There are some important rules that we need to follow for IUPAC naming.In order to name organic
compounds you must first memorize a few basic names. These names are listed within the discussion of
naming alkanes. In general, the base part of the name reflects the number of carbons in what you have
assigned to be the parent chain. The suffix of the name reflects the type(s) of functional group(s) present
on (or within) the parent chain. Other groups which are attached to the parent chain are called
substituents.
A.Alkanes - saturated hydrocarbons
The names of the straight chain saturated hydrocarbons for up to a 12 carbon chain are shown below.
The names of the substituents formed by the removal of one hydrogen from the end of the chain is
obtained by changing the suffix -ane to -yl.
Number of Carbons Name
1 methane
2 ethane
3 propane
4 butane
5 pentane
6 hexane
7 heptane
8 octane
9 nonane
10 decane
11 undecane
12 dodecane
Here is a simple list of rules to follow. Some examples are given at the end of the list.
Identify the longest carbon chain. This chain is called the parent chain.
, Identify all of the substituents (groups appending from the parent chain).
Number the carbons of the parent chain from the end that gives the substituents the lowest numbers.
When compairing a series of numbers, the series that is the "lowest" is the one which contains the
lowest number at the occasion of the first difference. If two or more side chains are in equivalent
positions, assign the lowest number to the one which will come first in the name.
If the same substituent occurs more than once, the location of each point on which the substituent
occurs is given. In addition, the number of times the substituent group occurs is indicated by a prefix (di,
tri, tetra, etc.).
If there are two or more different substituents they are listed in alphabetical order using the base name
(ignore the prefixes). The only prefix which is used when putting the substituents in alphabetical order is
iso as in isopropyl or isobutyl. The prefixes sec- and tert- are not used in determining alphabetical order
except when compared with each other.
If chains of equal length are competing for selection as the parent chain, then the choice goes in series
to:
a) the chain which has the greatest number of side chains.
b) the chain whose substituents have the lowest- numbers.
c) the chain having the greatest number of carbon atoms in the smaller side chain.
d)the chain having the least branched side chains.
A cyclic (ring) hydrocarbon is designated by the prefix cyclo- which appears directly in front of the base
name.
Example 1
Let's start with a simple example. To name this compound, we need to first find the longest continuous
carbon chain, which is these two carbons here.
Number the chain forward and backward.
Count the number of carbons in the chain.
Based on the number of carbons, determine the prefix for the compound name.
Determine the type of bond between the carbon atoms.
Combine the prefix and the bond type to get the IUPAC name.
In this example, the compound has two carbons, so the name will start with "eth-". Since there is a
single bond between the carbon atoms, it is an alkane, so the name will end with "-ane". Therefore, the
IUPAC name of this compound is "ethane".
