IUPAC Name, Structure and Formula of Straight-Chain Primary Alkanamides (amides) Chemistry Tutorial
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 |
|---|
|
|
|
- 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 name(2) 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: | 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 | 10 |
|---|
| Prefix: | meth | eth | prop | but | pent | hex | hept | oct | non | dec |
|---|
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Structure and Bonding of Primary Alkanamides (amides)
Primary alkanamides are amides, and are compounds containing ONLY carbon, hydrogen, oxygen and nitrogen atoms.
Primary alkanamides contain the C(O)-NH2 functional group, known as the amide functional group.
- Carbon belongs to group 14 in the periodic table.
Each carbon atom in the primary alkanamide molecule has 4 valence electrons.
- Oxygen belongs to group 16 in the periodic table.
Each oxygen atom in the primary alkanamide molecule has 6 valence electrons.
- Each hydrogen atom in the primary alkanamide molecule has 1 valence electron.
- Nitrogen belongs to group 15 in the periodic table.
Each nitrogen atom in the primary alkanamide molecule has 5 valence electrons.
- Each amide (C(O)-NH2) functional group is made up of 1 atom of carbon sharing two pairs of electrons with an oxygen atom and one pair of electrons with a nitrogen atom:
Note that the oxygen atom now has a share in 8 valence electrons in total.
The nitrogen atom still has two unpaired electrons.
In a primary alkanamide these electrons will pair up with electrons from hydrogen atoms:
- The unpaired electron around the carbon atom can now pair up with an electron from another carbon atom or from a hydrogen atom in order to produce a primary alkanamide molecule.
- Note that the C(O)-NH2 group will always be at the end of a chain of carbon atoms because the carbon of the C(O)-NH2 group has only 1 electron to share.
Steps for IUPAC Naming of Straight Chain Primary Alkanamides (amides)
- 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: | 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 | 10 |
|---|
| Prefix: | meth | eth | prop | but | pent | hex | hept | oct | non | dec |
|---|
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
Worked Example of IUPAC Naming of Straight Chain Primary Alkanamide: 1 Carbon Atom Chain
Name the straight chain primary alkanamine shown below using IUPAC nomenclature rules:
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.
systematic
(number of carbon atoms) |
|
preferred IUPAC
(parent alkanoic acid without the "ic acid" ending) |
| 1 carbon atom in the chain
Prefix is methan
|
|
Parent alkanoic acid is formic acid
Prefix is form |
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
systematic
(number of carbon atoms) |
|
preferred IUPAC
(parent alkanoic acid without the "ic acid" ending) |
| methanamide |
|
formamide |
Worked Example of IUPAC Name of a Straight-Chain Primary Alkanamide: 2 Carbon Atom Chain
Name the straight chain primary alkanamide shown below using IUPAC nomenclature rules:
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.
systematic
(number of carbon atoms) |
|
preferred IUPAC
(parent alkanoic acid without the "ic acid" ending) |
| 2 carbon atoms in the chain
Prefix is ethan
|
|
parent alkanoic acid is acetic acid
Prefix is acet |
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
systematic
(number of carbon atoms) |
|
preferred IUPAC
(parent alkanoic acid without the "ic acid" ending) |
| ethanamide |
|
acetamide |
Worked Example of IUPAC Naming of a Straight-Chain Primary Alkanamide: 3 Carbon Atom Chain
Name the straight chain primary alkanamide shown below using IUPAC nomenclature rules:
| | 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 Structure(3) 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.
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.
Worked Example of Drawing the Structure of a Straight-Chain Primary Alkanamide
Draw a structure for the straight chain primary alkanamide butanamide using IUPAC nomenclature rules.
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.
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(4).
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.
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O
|| |
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| H- |
N |
- |
C |
- |
C |
- |
C |
- |
C |
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H |
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Step 5: Draw dashes around each remaining carbon atom such that each carbon atom makes 4 bonds.
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O
|| |
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| |
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| |
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| H- |
N |
- |
C |
- |
C |
- |
C |
- |
C |
- |
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H |
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Step 6: Complete the structure by placing a hydrogen atom (H) at the end of all the vacant dashes.
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O
|| |
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H
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H
| |
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H
| |
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| H- |
N |
- |
C |
- |
C |
- |
C |
- |
C |
-H |
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H |
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H |
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H |
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H |
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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 O(5):
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)
Worked Example of Writing the Molecular Formula of a Straight-Chain Primary Alkanamide
Write the molecular formula for butanamide.
Step 1: Draw the structure of the alkanamide molecule.
| |
H
| |
|
H
| |
|
H
| |
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O
|| |
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|
| H- |
C |
- |
C |
- |
C |
- |
C |
- |
N |
-H |
| |
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H |
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H |
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H |
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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
| |
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H
| |
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H
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O
|| |
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| H- |
C4 |
- |
C3 |
- |
C2 |
- |
C1 |
- |
N |
-H |
| |
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H |
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H |
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H |
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H |
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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
| |
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3H
| |
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4H
| |
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O
|| |
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| 1H- |
C |
- |
C |
- |
C |
- |
C |
- |
N |
-H5 |
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H9 |
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H8 |
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H7 |
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H6 |
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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
| |
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H
| |
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H
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O
|| |
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| H- |
C |
- |
C |
- |
C |
- |
C |
- |
N1 |
-H |
| |
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H |
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H |
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H |
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H |
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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
| |
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H
| |
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H
| |
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1O
|| |
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| H- |
C |
- |
C |
- |
C |
- |
C |
- |
N |
-H |
| |
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H |
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H |
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H |
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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 × 4 + 1 = 9
number of nitrogen atoms = number of oxygen atoms = 1
Summay Table: Molecular Formula, Structure and IUPAC Name of Some Primary Alkanamides
no. C atoms
(n) |
Molecular Formula
CnH2n+1NO |
Structure |
Preferred IUPAC Name
(alternative name) |
| 1 |
CH3NO |
|
formamide
(methanamide) |
|
| 2 |
C2H5NO |
| |
H
| |
|
O
|| |
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|
| H- |
C |
- |
C |
- |
N |
-H |
| |
|
H |
|
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|
H |
|
|
acetamide
(ethanamide) |
|
| 3 |
C3H7NO |
| |
H
| |
|
H
| |
|
O
|| |
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|
|
| H- |
C |
- |
C |
- |
C |
- |
N |
-H |
| |
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H |
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H |
|
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H |
|
|
propanamide |
|
| 4 |
C4H9NO |
| |
H
| |
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H
| |
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H
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O
|| |
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| H- |
C |
- |
C |
- |
C |
- |
C |
- |
N |
-H |
| |
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H |
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H |
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H |
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H |
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butanamide |
|
| 5 |
C5H11NO |
| |
H
| |
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H
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H
| |
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H
| |
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O
|| |
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| H- |
C |
- |
C |
- |
C |
- |
C |
- |
C |
- |
N |
-H |
| |
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H |
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H |
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H |
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H |
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H |
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pentanamide |
|
| 6 |
C6H13NO |
| |
H
| |
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H
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H
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H
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H
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O
|| |
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| H- |
C |
- |
C |
- |
C |
- |
C |
- |
C |
- |
C |
- |
N |
-H |
| |
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H |
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H |
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H |
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H |
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H |
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H |
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hexanamide |
|
| 7 |
C7H15NO |
| |
H
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H
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H
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H
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H
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H
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O
|| |
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| H- |
C |
- |
C |
- |
C |
- |
C |
- |
C |
- |
C |
- |
C |
- |
N |
-H |
| |
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H |
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H |
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H |
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H |
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H |
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H |
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H |
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heptanamide |
|
| 8 |
C8H17NO |
| |
H
| |
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H
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H
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H
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H
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H
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H
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O
|| |
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| H- |
C |
- |
C |
- |
C |
- |
C |
- |
C |
- |
C |
- |
C |
- |
C |
- |
N |
-H |
| |
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H |
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H |
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H |
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H |
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H |
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H |
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H |
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H |
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octanamide |
|
| 9 |
C9H19NO |
| |
H
| |
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H
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H
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H
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H
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H
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H
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H
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O
|| |
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| H- |
C |
- |
C |
- |
C |
- |
C |
- |
C |
- |
C |
- |
C |
- |
C |
- |
C |
- |
N |
-H |
| |
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H |
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H |
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H |
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H |
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H |
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H |
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H |
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H |
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H |
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nonanamide |
|
| 10 |
C10H21NO |
| |
H
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H
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H
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H
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H
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H
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H
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H
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H
| |
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O
|| |
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| H- |
C |
- |
C |
- |
C |
- |
C |
- |
C |
- |
C |
- |
C |
- |
C |
- |
C |
- |
C |
- |
N |
-H |
| |
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H |
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H |
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H |
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H |
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H |
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H |
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H |
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H |
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H |
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H |
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decanamide |
Footnotes:
(1) The 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.
(2) IUPAC 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
(4) We 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 CO-NH nor CO-N.
(5) The 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.
