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Naming Straight-Chain Primary Alkanamines

Key Concepts

  • Alkanamines are organic molecules containing only carbon (C), hydrogen (H) and nitrogen (N) atoms.

  • Alkanamines belong to the group of organic compounds known as amines.

  • Amines are derivatives of ammonia, NH3, in which carbon chains replace hydrogen atoms.

  • Primary alkanamines occur when only one of the hydrogen atoms in ammonia has been replaced by a carbon chain.

    R-NH2

  • Primary alkanamines contain the NH2, amine (amino) 1, functional group.

  • A primary alkanamine consists of a chain of 1 or more carbon atoms joined to each other by single covalent bonds, with an NH2 functional group attached to one of the carbon atoms in the chain.

  • The systematic IUPAC name2 of an alkan-n-amine is made up of three parts:

        (i) a prefix or stem
            (the name of the parent hydrocarbon (the alkane chain) without the "e" ending, alkan)

        (ii) an infix
            (a number which tells us the location of the NH2 functional group, -n-)

        (iii) a suffix
            (last part of the name, amine)

  • The suffix when naming a primary alkanamine is always "amine"

  • The prefix or stem is dependent on the number of carbon atoms in the longest chain of carbon atoms (the parent hydrocarbon, or parent alkane):
    Number of carbon atoms:12345678910
    Prefix:methethpropbutpenthexheptoctnondec

Steps for Naming Straight Chain Primary Alkanamines

  • The systematic IUPAC name of an alkan-n-amine is made up of three parts:

        (i) a prefix or stem (first part of the name, the name of the parent alkane without the "e" ending) : alkan

        (ii) an infix (a number indicating the location of the NH2 functional group) : -n-

        (iii) a suffix (last part of the name indicating the presence of the NH2 functional group) : amine

  • The name of a primary alkanamine always ends in the suffix amine

  • The first part of the name of a primary alkanamine, its prefix or stem, is determined by the number of carbon atoms in the parent alkane chain:

    Number of carbon atoms:12345678910
    Prefix:methethpropbutpenthexheptoctnondec

Step 1: Identify the longest carbon chain containing the NH2 (amine or amino) functional group.

Step 2: Determine the prefix for the name of the primary alkanamine based on the number of carbon atoms in the chain.
(The name of the parent alkane without the "e" ending)

Step 3: Number each carbon atom along the longest carbon chain so that the carbon atom bonded to the NH2 (amine or amino) functional group has the lowest possible number.

Step 4: Determine the infix for the name of the primary alkanamine based on the location of the NH2 (amine or amino) functional group.

Note that the infix may not be required if the longest carbon chain contains only one or two carbon atoms.

Step 5: Determine the suffix for the name of the primary alkanamine. All primary alkanamines containing one NH2 (amine or amino) functional group will end in "amine".

Step 6: Write the name for the primary alkanamine in the form of prefix-infix-suffix

Example

Name the straight chain primary alkanamine shown below:

 H
|
 H
|
 H
|
  
H-C-C-C-NH2
 |
H
 |
H
 |
H
  

Step 1: Identify the longest carbon chain containing the NH2 (amine or amino) functional group.

 H
|
 H
|
 H
|
  
H-C-C-C-NH2
 |
H
 |
H
 |
H
  

Step 2: Determine the prefix for the name of the primary alkanamine based on the number of carbon atoms in the chain.
(The name of the parent alkane without the "e" ending)

3 carbon atoms in the chain so the parent alkane is propane
Prefix is propan

Step 3: Number each carbon atom along the longest carbon chain so that the carbon atom bonded to the NH2 (amine or amino) functional group has the lowest possible number.

 H
|
 H
|
 H
|
  
H-C3-C2-C1-NH2
 |
H
 |
H
 |
H
  

Step 4: Determine the infix for the name of the primary alkanamine based on the location of the NH2 (amine or amino) functional group.

Note that the infix may not be required if the longest carbon chain contains only one or two carbon atoms.

There are 3 carbon atoms in the chain so an infix IS required.
NH2 group is bonded to carbon 1
Infix is -1-

Step 5: Determine the suffix for the name of the primary alkanamine. All primary alkanamines containing one NH2 (amine or amino) functional group will end in "amine".

Suffix is amine

Step 6: Write the name for the primary alkanamine in the form of prefix-infix-suffix

propan-1-amine

Steps for Drawing the Structure3 of Straight Chain Primary Alkanamines

Step 1: Break the systematic IUPAC name of the alkan-n-amine into its three parts:

alkan -n- amine
prefix infix suffix

Note that the infix may be absent if the parent alkane chain contains only 1 or 2 carbon atoms.

Step 2: Determine the number of carbon atoms in the longest alkane carbon chain using the prefix.

Step 3: Draw a chain of carbon atoms of the required length using dashes to represent a single covalent bond between each pair of carbon atoms.

Step 4: Draw dashes around each carbon atom in the chain such that each carbon atom makes 4 bonds.

Step 5: Number the carbon atoms in the chain from left to right.

Step 6: Determine the location of the NH2 (amine or amino) functional group using the infix.
We know there is an NH2 functional group because the molecule's name has the suffix amine4.

Step 7: Draw the NH2 group at the end of a dash on the carbon with the same number as the infix.

Step 8: Complete the structure by placing a hydrogen atom (H) at the end of all the vacant dashes.

Example

Draw a structure for the straight chain primary alkanamine propan-2-amine (2-propanamine).

Step 1: Break the systematic IUPAC name of the alkan-n-amine into its three parts:

alkan -n- amine
prefix infix suffix
propan -2- amine

Step 2: Determine the number of carbon atoms in the longest alkane carbon chain using the prefix.

Prefix is propan therefore there are 3 carbon atoms in the chain.

Step 3: Draw a chain of carbon atoms of the required length using dashes to represent a single covalent bond between each pair of carbon atoms.

C - C - C

Step 4: Draw dashes around each carbon atom in the chain such that each carbon atom makes 4 bonds.

  |   |   |  
- C - C - C -
  |   |   |  

Step 5: Number the carbon atoms in the chain from left to right.

  |   |   |  
- C1 - C2 - C3 -
  |   |   |  

Step 6: Determine the location of the NH2 (amine or amino) functional group using the infix.
We know there is an NH2 functional group because the molecule's name has the suffix amine4.

Infix is -2- so the NH2 group is bonded to carbon number 2 in the chain.

Step 7: Draw the NH2 group at the end of a dash on the carbon with the same number as the infix.

 
|
  NH2
|
 
|
 
- C1 - C2 - C3 -
  |   |   |  

Step 8: Complete the structure by placing a hydrogen atom (H) at the end of all the vacant dashes.

  H
|
  NH2
|
  H
|
 
H- C - C - C -H
  |
H
  |
H
  |
H
 
or
  H       H  
    \   /    
  H
|
  N
|
  H
|
 
H- C - C - C -H
  |
H
  |
H
  |
H
 

Steps for Writing the Molecular Formula of Straight Chain Primary Alkanamines

A molecular formula tells us the number of atoms of each element present in a molecule of the compound.

For a straight-chain primary alkanamine, only three elements are present, carbon (C), hydrogen (H) and nitrogen (N).

When writing the molecular formula of an alkanamine, the number of carbon atoms is written before the number of hydrogen atoms which is written before the number of oxygen atoms, that is, C is written before H which is written before N5:

CxHyN

Step 1: Draw the structure of the alkan-n-amine molecule.

Step 2: Write a skeleton molecular formula using the symbols for carbon (C), hydrogen (H) and nitrogen (N).

C H N

Step 3: Count the number of carbon atoms in the alkanamine molecule.

Step 4: Write the number of of carbon atoms into the skeleton molecular formula as a subscript number to the right of the symbol for carbon (C).

Step 5: Count the number of hydrogen atoms in the alkanamine molecule.

Step 6: Write the number of of hydrogen atoms into the skeleton molecular formula as a subscript number to the right of the symbol for hydrogen (H).

Step 7: Count the number of nitrogen atoms in the alkanamine molecule.

Step 8: Write the number of of nitrogen atoms into the skeleton molecular formula as a subscript number to the right of the symbol for nitrogen (N).
    Note: if only one amine (or amino, NH2) group is present, the number of nitrogen atoms is 1, and the subscript 1 is NOT included in the molecular formula.

Step 9: Check that your completed molecular formula makes sense (for a straight chain primary alkanamine CnH2n+3N)

Example

Write the molecular formula for butan-2-amine (2-butanamine).

Step 1: Draw the structure of the alkan-n-amine molecule.

  H       H      
    \   /        
  H   N   H   H  
  |   |   |   |  
H- C - C - C - C -H
  |   |   |   |  
  H   H   H   H  

Step 2: Write a skeleton molecular formula using the symbols for carbon (C), hydrogen (H) and nitrogen (N).

C H N

Step 3: Count the number of carbon atoms in the alkanamine molecule.

  H       H      
    \   /        
  H   N   H   H  
  |   |   |   |  
H- C1 - C2 - C3 - C4 -H
  |   |   |   |  
  H   H   H   H  

Step 4: Write the number of of carbon atoms into the skeleton molecular formula as a subscript number to the right of the symbol for carbon (C).

C4H N

Step 5: Count the number of hydrogen atoms in the alkanamine molecule.

  H1       H2      
    \   /        
  H11   N   H3   H4  
  |   |   |   |  
10H- C - C - C - C -H5
  |   |   |   |  
  H9   H8   H7   H6  

Step 6: Write the number of of hydrogen atoms into the skeleton molecular formula as a subscript number to the right of the symbol for hydrogen (H).

C4H11N

Step 7: Count the number of nitrogen atoms in the alkanamine molecule:

  H       H      
    \   /        
  H   N1   H   H  
  |   |   |   |  
H- C - C - C - C -H
  |   |   |   |  
  H   H   H   H  

Step 8: Write the number of of nitrogen atoms into the skeleton molecular formula as a subscript number to the right of the symbol for nitrogen (N).
    Note: if only one amine (or amino, NH2) group is present, the number of nitrogen atoms is 1, and the subscript 1 is NOT included in the molecular formula.

Only 1 nitrogen atom is present in this molecule so no subscript 1 is required in the molecular formula.

Molecular formula for butan-2-amine is C4H11N

Step 9: Check that your completed molecular formula makes sense (CnH2n+3N for primary alkanamines)
n = number of carbon atoms = 4
number of hydrogen atoms = 2 x n + 3 = 2 x 4 + 3 = 11
number of nitrogen atoms = 1

Summay Table: Molecular Formula, Structure and Name of Some Primary Alkanamines

no. C atoms
(n)
Molecular Formula
CnH2n+3N
Structure Preferred IUPAC Name
1 CH5N
    H       H
    |     /  
H - C - N    
    |     \  
    H       H
methanamine

2 C2H7N
    H   H       H
    |   |     /  
H - C - C - N    
    |   |     \  
    H   H       H
ethanamine

3 C3H9N
    H   H   H       H
    |   |   |     /  
H - C - C - C - N    
    |   |   |     \  
    H   H   H       H
propan-1-amine
    H       H    
      \   /      
    H
|
  N
|
  H
|
   
H - C - C - C - H
    |
H
  |
H
  |
H
   
propan-2-amine

4 C4H11N
    H
|
  H
|
  H
|
  H
|
    H
/
 
H - C - C - C - C - N    
    |
H
  |
H
  |
H
  |
H
    \
H
 
butan-1-amine
          H
\
  H
/
     
    H
|
  H
|
  N
|
  H
|
   
H - C - C - C - C - H
    |
H
  |
H
  |
H
  |
H
   
butan-2-amine

5 C5H13N
    H
|
  H
|
  H
|
  H
|
  H
|
    H
/
H - C - C - C - C - C - N  
    |
H
  |
H
  |
H
  |
H
  |
H
    \
H
pentan-1-amine
              H
\
  H
/
     
    H
|
  H
|
  H
|
  N
|
  H
|
   
H - C - C - C - C - C - H
    |
H
  |
H
  |
H
  |
H
  |
H
   
pentan-2-amine
          H
\
  H
/
         
    H
|
  H
|
  N
|
  H
|
  H
|
   
H - C - C - C - C - C - H
    |
H
  |
H
  |
H
  |
H
  |
H
   
pentan-3-amine

6 C6H15N
    H
|
  H
|
  H
|
  H
|
  H
|
  H
|
    H
/
H - C - C - C - C - C - C - N  
    |
H
  |
H
  |
H
  |
H
  |
H
  |
H
    \
H
hexan-1-amine
                  H
\
  H
/
     
    H
|
  H
|
  H
|
  H
|
  N
|
  H
|
   
H - C - C - C - C - C - C - H
    |
H
  |
H
  |
H
  |
H
  |
H
  |
H
   
hexan-2-amine
              H
\
  H
/
         
    H
|
  H
|
  H
|
  N
|
  H
|
  H
|
   
H - C - C - C - C - C - C - H
    |
H
  |
H
  |
H
  |
H
  |
H
  |
H
   
hexan-3-amine

7 C7H17N
    H
|
  H
|
  H
|
  H
|
  H
|
  H
|
  H
|
    H
/
H - C - C - C - C - C - C - C - N  
    |
H
  |
H
  |
H
  |
H
  |
H
  |
H
  |
H
    \
H
heptan-1-amine
                      H
\
  H
/
     
    H
|
  H
|
  H
|
  H
|
  H
|
  N
|
  H
|
   
H - C - C - C - C - C - C - C - H
    |
H
  |
H
  |
H
  |
H
  |
H
  |
H
  |
H
   
heptan-2-amine
                  H
\
  H
/
         
    H
|
  H
|
  H
|
  H
|
  N
|
  H
|
  H
|
   
H - C - C - C - C - C - C - C - H
    |
H
  |
H
  |
H
  |
H
  |
H
  |
H
  |
H
   
heptan-3-amine
              H
\
  H
/
             
    H
|
  H
|
  H
|
  N
|
  H
|
  H
|
  H
|
   
H - C - C - C - C - C - C - C - H
    |
H
  |
H
  |
H
  |
H
  |
H
  |
H
  |
H
   
heptan-4-amine

8 C8H19N
    H
|
  H
|
  H
|
  H
|
  H
|
  H
|
  H
|
  H
|
    H
/
H - C - C - C - C - C - C - C - C - N  
    |
H
  |
H
  |
H
  |
H
  |
H
  |
H
  |
H
  |
H
    \
H
octan-1-amine
                          H
\
  H
/
     
    H
|
  H
|
  H
|
  H
|
  H
|
  H
|
  N
|
  H
|
   
H - C - C - C - C - C - C - C - C - H
    |
H
  |
H
  |
H
  |
H
  |
H
  |
H
  |
H
  |
H
   
octan-2-amine
                      H
\
  H
/
         
    H
|
  H
|
  H
|
  H
|
  H
|
  N
|
  H
|
  H
|
   
H - C - C - C - C - C - C - C - C - H
    |
H
  |
H
  |
H
  |
H
  |
H
  |
H
  |
H
  |
H
   
octan-3-amine
                  H
\
  H
/
             
    H
|
  H
|
  H
|
  H
|
  N
|
  H
|
  H
|
  H
|
   
H - C - C - C - C - C - C - C - C - H
    |
H
  |
H
  |
H
  |
H
  |
H
  |
H
  |
H
  |
H
   
octan-4-amine


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1The NH2 functional group in primary amines is called the amine group or amino group.
If the NH2 functional group is the only functional group present, or, if the NH2 group is the functional group with the highest seniority, then the molecule is named with the amine suffix.
Note that when another functional group takes precedence over the NH2 functional group, the NH2 group is then named as the amino group and becomes a prefix.

2IUPAC is the abbreviation for the International Union of Pure and Applied Chemistry

The preferred IUPAC systematic name is the substitutive name and places the infix for the locant immediately before that part of the name to which it relates, except when the preferred IUPAC name is the traditional contracted name in which case the infix is placed at the front of the name.
For the simple primary alkanamines we are discussing, either nomenclature is acceptable since the name in each case is unambiguous.
It is also common to see amines named using the IUPAC functional class naming system, but this is not the preferred nomenclature. In functional class nomenclature the suffix "amine" is preceded by the name of the alkyl chain so that the name is of the form alkylamine.
The systematic IUPAC name is derived from a set of general "rules" designed to ensure that each organic molecule can be given an unambiguous name.
The rules for naming organic compounds are still being developed. The most recent document for referral is "Preferred names in the nomenclature of organic compounds" (Draft 7 October 2004).

3"Structure" here will refer to a valence structure, which can be used to represent the 2-dimensional structural formula.

Once you have drawn the valence structure or 2-dimensional structural formula you can use this to draw

a condensed (semi) structural formula

or a skeletal structure

4We know this is a primary alkanamine because there is no "N" locant in the name, hence the functional group of the amine is NH2 and not NH nor N.

5The molecular formula of a straight chain primary alkanamine is CnH2n+3N, while the often used CnH2n+1NH2 is, strictly speaking, not a molecular formula but a condensed structural formula.

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