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Naming Straight-Chain Primary Alkanamides

Key Concepts

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

  • Alkanamides belong to the group of organic compounds known as amides.

  • Amides are named as derivatives of the corresponding carboxylic acid.

  • In primary alkanamides, an NH2 group replaces the OH group in the alkanoic acid:

    alkanoic acid primary alkanamide
        O
        //  
    R-C    
        \  
        O-H
        O  
        //    
    R-C      
        \    
        N -H
        |
    H
     

  • Primary alkanamides contain the C(O)-NH2, amide 1, functional group.

  • A primary alkanamide consists of a chain of 1 or more carbon atoms joined to each other by single covalent bonds.
    The amide, C(O)-NH2, functional group is attached to the first of the carbon atoms in the chain.

  • The systematic IUPAC name2 of a primary alkanamide is made up of two parts:

        (i) a prefix or stem
            (the name of the parent alkanoic acid without the "oic acid" ending, alkan)

        (ii) a suffix
            (last part of the name, amide)

  • The suffix when naming a straight chain primary alkanamide is always "amide"

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

Steps for Naming Straight Chain Primary Alkanamides

  • The systematic IUPAC name of a primary alkanamide is made up of two parts:

        (i) a prefix or stem (first part of the name, the name of the parent alkanoic acid without the "oic acid" ending) : alkan

        (ii) a suffix (last part of the name indicating the presence of the terminal (end) C(O)-NH2 functional group) : amide

  • The name of a primary alkanamide always ends in the suffix amide

  • The first part of the name of a primary alkanamide, 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 terminal (end) C(O)-NH2 (amide) functional group.

Step 2: Determine the prefix for the name of the primary alkanamide based on the number of carbon atoms in the chain.
(The name of the parent alkanoic acid without the "oic acid" ending)

Step 3: Determine the suffix for the name of the primary alkanamide. All primary alkanamides containing one C(O)-NH2 (amide) functional group will end in "amide".

Step 4: Write the name for the primary alkanamide in the form of prefixsuffix

Example: 3 Carbon Atom Chain

Name the straight chain primary alkanamide shown below:

 H
|
 H
|
 O
||
   
H-C-C-C-N-H
 |
H
 |
H
   |
H
 

Step 1: Identify the longest carbon chain containing the terminal (end) C(O)-NH2 (amide) functional group.

 H
|
 H
|
 O
||
   
H-C-C-C-N-H
 |
H
 |
H
   |
H
 

Step 2: Determine the prefix for the name of the primary alkanamide based on the number of carbon atoms in the chain.

systematic
(number of carbon atoms)
  preferred IUPAC
(parent alkanoic acid without the "ic acid" ending)
3 carbon atoms in the chain

Prefix is propan

  parent alkanoic acid is propanoic acid

Prefix is propan

Step 3: Determine the suffix for the name of the primary alkanamide.

All primary alkanamides containing one C(O)-NH2 (amide) functional group will end in "amide".

Suffix is amide

Step 4: Write the name for the primary alkanamide in the form of prefixsuffix

propanamide

Steps for Drawing the Structure3 of Straight Chain Primary Alkanamides

Step 1: Break the systematic IUPAC name of the primary alkanamide into its two parts:

alkan amide
prefix suffix

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: For the "amide" suffix, on the first C atom, draw 2 vertical lines connected to an O atom (representing the double bonded oxygen), and one horizontal line to the left to a N atom.
Draw another horizontal line to the left from the N atom to a H atom, and a vertical line from the N atom to another H atom.

Step 5: Draw dashes around each remaining carbon atom such that each carbon atom makes 4 bonds.

Step 6: 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 alkanamide butanamide.

Step 1: Break the systematic IUPAC name of the primary alkanamide into its two parts:

prefix suffix
butan amide

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

Prefix is butan so there are 4 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 - C

Step 4: For the "amide" suffix, on the first C atom, draw 2 vertical lines connected to an O atom (representing the double bonded oxygen), and one horizontal line to the left to a N atom4.
Draw another horizontal line to the left from the N atom to a H atom, and a vertical line from the N atom to another H atom.

      O
||
           
H- N - C - C - C - C
  |
H
               

Step 5: Draw dashes around each remaining carbon atom such that each carbon atom makes 4 bonds.

      O
||
  |   |   |  
H- N - C - C - C - C -
  |
H
      |   |   |  

Step 6: Complete the structure by placing a hydrogen atom (H) at the end of all the vacant dashes.

      O
||
  H
|
  H
|
  H
|
 
H- N - C - C - C - C -H
  |
H
      |
H
  |
H
  |
H
 

Steps for Writing the Molecular Formula of Straight Chain Primary Alkanamides

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

For a straight-chain primary alkanamide, only four elements are present, carbon (C), hydrogen (H), nitrogen (N) and oxygen (O).

When writing the molecular formula of an alkanamide, the number of carbon atoms is written before the number of hydrogen atoms which is written before the number of nitrogen atoms which is written before the number of oxygen atoms, that is, C is written before H which is written before N which is written before O5:

CxHyNO

Step 1: Draw the structure of the alkanamide molecule.

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

C H N O

Step 3: Count the number of carbon atoms in the alkanamide 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 alkanamide 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 alkanamide 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 amide group is present, the number of nitrogen atoms is 1, and the subscript 1 is NOT included in the molecular formula.

Step 9: Count the number of oxygen atoms in the alkanamide molecule.

Step 10: Write the number of of oxygen atoms into the skeleton molecular formula as a subscript number to the right of the symbol for oxygen (O).
    Note: if only one amide group is present, the number of oxygen atoms is 1, and the subscript 1 is NOT included in the molecular formula.

Step 11: Check that your completed molecular formula makes sense (for a straight chain primary alkanamide CnH2n+1NO)

Example

Write the molecular formula for butanamide.

Step 1: Draw the structure of the alkanamide molecule.

  H
|
  H
|
  H
|
  O
||
     
H- C - C - C - C - N -H
  |
H
  |
H
  |
H
      |
H
 

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

C H N O

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

  H
|
  H
|
  H
|
  O
||
     
H- C4 - C3 - C2 - C1 - N -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 O

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

  2H
|
  3H
|
  4H
|
  O
||
     
1H- C - C - C - C - N -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).

C4H9N O

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

  H
|
  H
|
  H
|
  O
||
     
H- C - C - C - C - N1 -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).
    Only one amide group is present, the number of nitrogen atoms is 1, and the subscript 1 is NOT included in the molecular formula.

C4H9NO

Step 9: Count the number of oxygen atoms in the alkanamide molecule.

  H
|
  H
|
  H
|
  1O
||
     
H- C - C - C - C - N -H
  |
H
  |
H
  |
H
      |
H
 

Step 10: Write the number of of oxygen atoms into the skeleton molecular formula as a subscript number to the right of the symbol for oxygen (O).
    Only one amide group is present, the number of oxygen atoms is 1, and the subscript 1 is NOT included in the molecular formula.

C4H9NO

Step 11: Check that your completed molecular formula makes sense (for a straight chain primary alkanamide CnH2n+1NO)

number of carbon atoms = n = 4,
number of hydrogen atoms = 2n + 1 = 2 x 4 + 1 = 9
number of nitrogen atoms = number of oxygen atoms = 1

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

no. C atoms
(n)
Molecular Formula
CnH2n+1NO
Structure Preferred IUPAC Name
(alternative name)
1 CH3NO
    O
||
     
H - C - N -H
        |
H
 
formamide
(methanamide)

2 C2H5NO
  H
|
  O
||
     
H- C - C - N -H
  |
H
      |
H
 
acetamide
(ethanamide)

3 C3H7NO
  H
|
  H
|
  O
||
     
H- C - C - C - N -H
  |
H
  |
H
      |
H
 
propanamide

4 C4H9NO
  H
|
  H
|
  H
|
  O
||
     
H- C - C - C - C - N -H
  |
H
  |
H
  |
H
      |
H
 
butanamide

5 C5H11NO
  H
|
  H
|
  H
|
  H
|
  O
||
     
H- C - C - C - C - C - N -H
  |
H
  |
H
  |
H
  |
H
      |
H
 
pentanamide

6 C6H13NO
  H
|
  H
|
  H
|
  H
|
  H
|
  O
||
     
H- C - C - C - C - C - C - N -H
  |
H
  |
H
  |
H
  |
H
  |
H
      |
H
 
hexanamide

7 C7H15NO
  H
|
  H
|
  H
|
  H
|
  H
|
  H
|
  O
||
     
H- C - C - C - C - C - C - C - N -H
  |
H
  |
H
  |
H
  |
H
  |
H
  |
H
      |
H
 
heptanamide

8 C8H17NO
  H
|
  H
|
  H
|
  H
|
  H
|
  H
|
  H
|
  O
||
     
H- C - C - C - C - C - C - C - C - N -H
  |
H
  |
H
  |
H
  |
H
  |
H
  |
H
  |
H
      |
H
 
octanamide

9 C9H19NO
  H
|
  H
|
  H
|
  H
|
  H
|
  H
|
  H
|
  H
|
  O
||
     
H- C - C - C - C - C - C - C - C - C - N -H
  |
H
  |
H
  |
H
  |
H
  |
H
  |
H
  |
H
  |
H
      |
H
 
nonanamide

10 C10H21NO
  H
|
  H
|
  H
|
  H
|
  H
|
  H
|
  H
|
  H
|
  H
|
  O
||
     
H- C - C - C - C - C - C - C - C - C - C - N -H
  |
H
  |
H
  |
H
  |
H
  |
H
  |
H
  |
H
  |
H
  |
H
      |
H
 
decanamide


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1The C(O)-NH2 functional group in primary amides is called the amide group.
Note that when the C(O)-NH2 functional group is attached to a benzene ring, the suffix becomes carboxamide.

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 alkanamides we are discussing, no infix is required because the C(O)-NH2 functional will ALWAYS be terminal.
Note that because the systematic IUPAC name is derived from the name of the corresponding carboxylic acid, methanamide has the preferred IUPAC name of formamide, and, ethanamide has the preferred IUPAC name of acetamide.
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 alkanamide because there is no "N" locant in the name, hence the functional group of the amide is C(O)-NH2 and not C(O)-NH nor C(O)-N.

5The molecular formula of a straight chain primary alkanamide is CnH2n+1NO, while the often used CnH2n+1CO-NH2 is, strictly speaking, not a molecular formula but a condensed structural formula.

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