Steps for Naming Straight Chain Alkanenitriles
- The systematic IUPAC name of an alkanenitrile is made up of two parts:
(i) a prefix or stem (the name of the parent alkane) : alkane
Note the exceptions:
⚛ methanenitrile has the preferred IUPAC name of formonitrile
⚛ ethanenitrile has the preferred IUPAC name of acetonitrile
(ii) a suffix (last part of the name indicating the presence of the CN functional group) : nitrile
- The name of a straight chain alkanenitrile always ends in the suffix nitrile
- The first part of the name of a straight chain alkanenitrle, 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 CN (cyano) functional group.
Step 2: Number each carbon atom along the longest carbon chain so that the carbon atom of the CN (cyano) functional group has the number 1.
Step 3: Determine the prefix for the name of the alkanenitrile based on the number of carbon atoms in the chain.
Step 4: Determine the suffix for the name of the alkanenitrile:
If only one CN (cyano) functional group is present, the name will end in "nitrile".
If there is a CN functional group at each end of the alkane chain, it is named as a "dinitrile".
Step 5: Write the name for the alkanenitrile in the form of prefixsuffix
Example: Alkanenitrile with 1 Carbon Atom
Name the straight chain alkanenitrile shown below:
H−C≡N
Step 1: Identify the longest carbon chain containing the CN (cyano) functional group.
H−C≡N
Step 2: Number each carbon atom along the longest carbon chain so that the carbon atom of the CN (cyano) functional group has the number 1.
H−C1≡N
Step 3: Determine the prefix for the name of the alkanenitrile based on the number of carbon atoms in the chain.
(The name of the parent alkane)
Longest carbon chain has 1 carbon atom.
Parent hydrocarbon is methane.
Prefix is methane
Step 4: Determine the suffix for the name of the alkanenitrile.
One CN (cyano) functional group, the name ends in "nitrile".
A CN functional group at each end of the alkane chain, the name ends in "dinitrile".
Suffix is nitrile
Step 5: Write the name for the alkanenitrile in the form of prefixsuffix
Systematic IUPAC name is methanenitrile
Note: Preferred IUPAC name is formonitrile.
Example: Alkanenitrile with 2 Carbon Atom Chain
Name the straight chain alkanenitrile shown below:
Step 1: Identify the longest carbon chain containing the CN (cyano) functional group.
Step 2: Number each carbon atom along the longest carbon chain so that the carbon atom of the CN (cyano) functional group has the number 1.
Step 3: Determine the prefix for the name of the alkanenitrile based on the number of carbon atoms in the chain.
Longest carbon chain has 2 carbon atoms.
Parent hydrocarbon is ethane.
Prefix is ethane
Step 4: Determine the suffix for the name of the alkanenitrile.
One CN (cyano) functional group, the name ends in "nitrile".
A CN functional group at each end of the alkane chain, the name ends in "dinitrile".
Suffix is nitrile
Step 5: Write the name for the alkanenitrile in the form of prefixsuffix
Systematic IUPAC name is ethanenitrile
Preferred IUPAC name is acetonitrile
Example: Alkanenitrile with 3 Carbon Atom Chain
Name the straight chain alkanenitrile shown below:
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H
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H
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| H− |
C |
− |
C |
− |
C≡N |
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H |
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H |
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Step 1: Identify the longest carbon chain containing the CN (cyano) functional group.
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H
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H
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| H− |
C |
− |
C |
− |
C≡N |
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H |
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H |
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Step 2: Number each carbon atom along the longest carbon chain so that the carbon atom of the CN (cyano) functional group has the number 1.
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H
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H
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| H− |
C3 |
− |
C2 |
− |
C1≡N |
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H |
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H |
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Step 3: Determine the prefix for the name of the alkanenitrile based on the number of carbon atoms in the chain.
Longest carbon chain has 3 carbon atoms.
Parent hydrocarbon is propane.
Prefix is propane
Step 4: Determine the suffix for the name of the alkanenitrile
One CN (cyano) functional group, the name ends in "nitrile".
A CN functional group at each end of the alkane chain, the name ends in "dinitrile".
Suffix is nitrile
Step 5: Write the name for the alkanenitrile in the form of prefixsuffix
Systematic IUPAC name is propanenitrile
(Preferred IUPAC name is also propanenitrile.)
Steps for Drawing the Structure(5) of Straight Chain Alkanenitrile
Step 1: Break the systematic IUPAC name of the alkanenitrile into its two parts:
| alkane |
nitrile |
| 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 "nitrile" suffix, on the first carbon atom, draw 3 horizontal lines stacked vertically and connected to a N atom (representing the triple bonded N atom, C≡N).
Step 5: Place dashes representing single covalent bonds around the other carbon atoms in the chain so that each of these carbon atoms is surrounded by 4 dashes.
Step 6: Complete the structure by placing a hydrogen atom (H) at the end of all the vacant dashes.
Example of Drawing the Structure of an Alkanenitrile
Draw a structure for butanenitrile.
Step 1: Break the systematic IUPAC name of the alkanenitrile into its two parts:
| butane |
nitrile |
| prefix |
suffix |
Step 2: Determine the number of carbon atoms in the longest alkane carbon chain using the prefix.
Prefix is butane, therefore this alkanenitrile has 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 "nitrile" suffix, on the first carbon atom, draw 3 horizontal lines stacked vertically and connected to a N atom (representing the triple bonded nitrogen atom, C≡N).
Step 5: Place dashes representing single covalent bonds around the other carbon atoms in the chain so that each of these carbon atoms is surrounded by 4 dashes.
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| N≡ |
C |
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C |
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C |
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C |
− |
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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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H
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H
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H
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| N≡ |
C |
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C |
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C |
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C |
−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 Alkanenitrile
A molecular formula tells us the number of atoms of each element present in a molecule of the compound.
For a straight-chain alkanenitrile, only three elements are present, carbon (C), hydrogen (H) and nitrogen (N).
When writing the molecular formula of an alkanenitrile, the number of carbon atoms is written before the number of hydrogen atoms which is written before the number of nitrogen atoms, that is, C is written before H which is written before N(6).
Step 1: Draw the structure of the alkanenitrile 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 alkanenitrile 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 alkanenitrile 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 alkanenitrile 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).
Step 9: Check that your completed molecular formula makes sense
(CnH2n-1N for an alkanenitrile)
Example
Write the molecular formula for pentanenitrile.
Step 1: Draw the structure of the alkanenitrile molecule.
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H |
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H |
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H |
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| N≡ |
C |
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C |
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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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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 alkanenitrile molecule.
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H |
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H |
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H |
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| N≡ |
C1 |
− |
C2 |
− |
C3 |
− |
C4 |
− |
C5 |
−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).
C5H N
Step 5: Count the number of hydrogen atoms in the alkanenitrile molecule.
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H1 |
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H2 |
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H3 |
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H4 |
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| N≡ |
C |
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C |
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C |
− |
C |
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C |
−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).
C5H9N
Step 7: Count the number of nitrogen atoms in the alkanenitrile molecule:
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H |
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H |
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H |
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| N1≡ |
C |
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C |
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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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Step 8: Write the number of nitrogen atoms into the skeleton molecular formula as a subscript number to the right of the symbol for nitrogen (N).
1 nitrogen atom is present in this molecule: C5H9N1
Note that when only 1 atom of an element is present in the molecule, we do not write a number in the molecular formula.
Molecular formula for pentanenitrile is therefore C5H9N
Step 9: Check that your completed molecular formula makes sense (for an alkanenitrile: CnH2n-1N)
n = number of carbon atoms = 5
number of hydrogen atoms = (2 × n) − 1 = (2 × 5) − 1 = 10 − 1 = 9
number of nitrogen atoms = 1
(1) There are different systems of IUPAC nomenclature.
IUPAC organic substitutive nomenclature results in a name that is just one word and ends with nitrile.
IUPAC organic functional class nomenclature results in a name that is two words, the last word being cyanide.
IUPAC inorganic nomenclature results in different names, for example, HCN can be named using hydrogen name nomenclature (hydrogen cyanide), additive nomenclature (hydridonitridocarbon) and substitutive nomenclature (methylidyneazane)
In this tutorial we will treat HCN as an organic molecule and use IUPAC substitutive nomenclature (which is actually based on an alkanoic acid parent, but we can use a hydrocarbon parent to simplify the process of naming of alkanenitriles)
(2) The CN functional group in alkanenitriles is called the cyano group.
If another functional group is more senior, it takes precedence over the cyano group in a molecule in assiging a suffix to the parent prefix, and cyano is used as the prefix.
If an unbranched alkane is linked to two or more terminal cyano functional groups, the suffix "carbonitrile" is used.
If the cyano functional group is attached to a benzene ring, for example, the molecule is named as a carbonitrile.
(3) IUPAC is the abbreviation for the International Union of Pure and Applied Chemistry
The preferred IUPAC systematic name 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 alkanenitriles we are discussing, no infix is required since the cyano group is, by definition, at the end of the carbon chain, the locant will always be 1 and the infix will always be 1.
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).
(4) When named by an organic chemist using IUPAC substitutive nomenclature rules, HCN would be named as methanenitrile, however, as a derivative of HCOOH which has the preferred IUPAC name formic acid (substitutive nomenclature name is methanoic acid), the "form" prefix is retained so HCN is formonitrile.
When HCN is named by an inorganic chemist using IUPAC systematic additive nomenclature it is called hydrogen(nitridocarbonate), but the traditional "hydrogen name" is hydrogen cyanide.
(5) "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
(6) The molecular formula of an alkanenitrile is CnH2n-1N, while the often used CxHyCN is, strictly speaking, not a molecular formula but a condensed structural formula, or a semi-structural formula in some cases.
