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Naming Straight-Chain Alkanediols

Key Concepts

  • Straight chain alkanediols are organic molecules containing only carbon (C), hydrogen (H) and oxygen (O) atoms.

  • Alkanediols belong to the group of organic compounds known as alcohols.

  • Alcohols are hydroxy compounds, they contain an OH, hydroxy (or hydroxyl)1, functional group.

  • A straight-chain alkanediol consists of a chain of 1 or more carbon atoms joined to each other by single covalent bonds, with two OH functional groups attached to either the same carbon atom in the chain, or, to two different carbon atoms in the chain.

  • Note that an alkanol contains only ONE hydroxyl, OH, functional group
    while an alkanediol contains TWO hydroxyl, OH, functional groups

  • The systematic IUPAC name2 of an alkane-n,n-diol is made up of three parts:

        (i) a prefix or stem
            (the name of the parent hydrocarbon (the alkane chain) alkane)

        (ii) an infix
            (two numbers which tell us the location of each of the OH functional groups, -n,n-)
            Note that the two numbers are separated by a comma
            Note that each number of the infix is separated from a letter by a hyphen

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

  • The suffix when naming a straight-chain alkanediol is always "diol"

  • 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

  • The general molecular formula for a straight-chain alkanediol is CnH2n+2O2

        where n = number of carbon atoms in the carbon chain

Steps for Naming Straight Chain Alkanediols

  • The systematic IUPAC name of an alkane-n,n-diol is made up of three parts:

        (i) a prefix or stem (first part of the name, the name of the parent alkane) : alkane

        (ii) an infix (two numbers indicating the location of each of the OH functional groups) : -n,n-

        (iii) a suffix (last part of the name indicating the presence of the TWO OH functional groups) : diol

  • The name of a straight chain alkanediol always ends in the suffix diol

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

    Number of carbon atoms:12345678910
    Prefix:methaneethanepropanebutanepentanehexaneheptaneoctanenonanedecane

Step 1: Identify the longest carbon chain containing both the OH (hydroxy or hydroxyl) functional groups.

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

Step 3: Number each carbon atom along the longest carbon chain so that the carbon atoms bonded to the OH (hydroxy or hydroxyl) functional groups have the lowest possible numbers.

For a straight chain alkanediol this means the first number will be the lowest possible.

Step 4: Determine the infix for the name of the alkanediol based on the location of the OH (hydroxy or hydroxyl) functional groups.

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

Write the infix with the lowest number first followed by a comma then followed by the larger number

Step 5: Determine the suffix for the name of the alkanediol.
All straight chain alkanediols will end in "diol".

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

Example: 1 Carbon Atom

Name the straight chain alkanediol shown below:

 H
|
  
H-C-OH
 |
OH
  

Step 1: Identify the longest carbon chain containing both the OH (hydroxy or hydroxyl) functional groups.

 H
|
  
H-C-OH
 |
OH
  

Step 2: Determine the prefix for the name of the alkanol 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 3: Number each carbon atom along the longest carbon chain so that the carbon atom bonded to the OH (hydroxy or hydroxyl) functional groups have the lowest possible numbers.

 H
|
  
H-C1-OH
 |
OH
  

Step 4: Determine the infix for the name of the alkanediol based on the location of both of the OH (hydroxy or hydroxyl) functional groups.

Note the infix is not required if the longest carbon chain contains only one carbon atoms.

This alkanediol has only 1 carbon atom so no infix is required.

Step 5: Determine the suffix for the name of the alkanediol.
All straight chain alkanediols will end in "diol".

Suffix is diol

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

Systematic IUPAC name is methanediol

Other names: 1,1-methanediol or methane-1,1-diol

Example: 2 Carbon Atom Chain

Name the straight chain alkanediol shown below:

 H
|
 H
|
  
H-C-C-OH
 |
H
 |
OH
  

Step 1: Identify the longest carbon chain containing both the OH (hydroxy or hydroxyl) functional groups.

 H
|
 H
|
  
H-C-C-OH
 |
H
 |
OH
  

Step 2: Determine the prefix for the name of the alkanediol 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 3: Number each carbon atom along the longest carbon chain so that the carbon atoms bonded to the OH (hydroxy or hydroxyl) functional groups have the lowest possible numbers.

chain numbered from right to left   chain numbered from left to right
 H
|
 H
|
  
H-C2-C1-OH
 |
H
 |
OH
  
 
 H
|
 H
|
  
H-C1-C2-OH
 |
H
 |
OH
  
Both OH groups attached to first carbon atom.
1 is less than 2
This numbering is preferred.
  Both OH groups attached to second carbon atom.
2 is greater than 1
This numbering is NOT preferred.

Step 4: Determine the infix for the name of the alkanediol based on the location of both of the OH (hydroxy or hydroxyl) functional groups.

Note that the infix is not required if the longest carbon chain contains only one carbon atom.

Both OH groups are attached to carbon 1

infix is -1,1-

Step 5: Determine the suffix for the name of the alkanediol.
All straight chain alkanediols will end in "diol".

Suffix is diol

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

Systematic IUPAC name is ethane-1,1-diol

Other names: 1,1-ethanediol

Example: 3 Carbon Atom Chain

Name the straight chain alkanediol shown below:

 H
|
 H
|
 H
|
  
H-C-C-C-OH
 |
H
 |
OH
 |
H
  

Step 1: Identify the longest carbon chain containing both of the OH (hydroxy or hydroxyl) functional groups.

 H
|
 H
|
 H
|
  
H-C-C-C-OH
 |
H
 |
OH
 |
H
  

Step 2: Determine the prefix for the name of the alkanol based on the number of carbon atoms in the chain.
(The name of the parent alkane)

Longest carbon chain has 3 carbon atoms.

Parent hydrocarbon is propane.

Prefix is propane

Step 3: Number each carbon atom along the longest carbon chain so that the carbon atoms bonded to the OH (hydroxy or hydroxyl) functional groups have the lowest possible numbers.

chain numbered from right to left   chain numbered from left to right
 H
|
 H
|
 H
|
  
H-C3-C2-C1-OH
 |
H
 |
OH
 |
H
  
 
 H
|
 H
|
 H
|
  
H-C1-C2-C3-OH
 |
H
 |
OH
 |
H
  
OH groups attached to first and second carbon atoms.
The first number of the infix will be 1.
This numbering is preferred.
  OH groups attached to second and third carbon atom.
The first number of the infix would be 2.
This numbering is NOT preferred because 2 is greater than 1

Step 4: Determine the infix for the name of the alkanediol based on the location of both of the OH (hydroxy or hydroxyl) functional groups.

Note the infix is not required if the longest carbon chain contains only one carbon atom.

 H
|
 H
|
 H
|
  
H-C-C2-C1-OH
 |
H
 |
OH
 |
H
  

Note that the infix is written such that the smaller number comes before the larger number, and a comma separates the two numbers from each other.

In this molecule, one OH group is attached to the first carbon atom in the chain, C1, and the other OH group is attached to the second carbon atom in the chain, C2, so the infix is -1,2-

Step 5: Determine the suffix for the name of the alkanediol.
All straight chain alkanediols will end in "diol".

Suffix is diol

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

Systematic IUPAC name is propane-1,2-diol

Other names: 1,2-propanediol

Steps for Drawing the Structure3 of Straight Chain Alkanediols

Step 1: Break the systematic IUPAC name of the alkane-n,n-diol into its three parts:

alkane -n,n- diol
prefix infix suffix

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

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 each of the OH (hydroxy or hydroxyl) functional groups using the infix.
We know there are two OH functional groups because the molecule's name has the suffix diol.

Step 7: Draw each OH 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 alkanediol ethane-1,2-diol (also known as ethylene glycol)

Step 1: Break the systematic IUPAC name of the alkane-n,n-diol into its three parts:

ethane -1,2- diol
alkane -n,n- diol
prefix infix suffix

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

Step 2: Determine the number of carbon atoms in the longest alkane carbon chain using the prefix.
Prefix is ethane
ethane indicates the parent alkane chain contains 2 carbon atoms with single covalent bonds between each carbon atom 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  

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

  |   |  
- C - C -
  |   |  

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

  |   |  
- C1 - C2 -
  |   |  

Step 6: Determine the location of each of the OH (hydroxy or hydroxyl) functional groups using the infix.
We know there are two OH functional groups because the molecule's name has the suffix diol.

infix is -1,2- therefore one OH group is attached to the first carbon atom in the ethane chain, and the second OH functional group is attached to the second carbon atom in the chain.

  |   |  
- C1 - C2 -
  |   |  

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

infix is -1,2- therefore one OH group is attached to the first carbon atom, and the other OH group is attached to the second atom in the ethane chain.

      OH  
  |   |      
HO- C1 - C2  -
  |   |      
OR
      O-H  
  |   |      
H-O- C1 - C2  -
  |   |      

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

  H     OH  
  |   |  
HO- C - C -H
  |   |  
  H   H  
OR
      H
|
 
  H   O  
  |   |  
H-O- C - C -H
  |   |  
  H   H  

Steps for Writing the Molecular Formula of Straight Chain Alkanediols

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

For a straight-chain alkanediol, only three elements are present, carbon (C), hydrogen (H) and oxygen (O).

When writing the molecular formula of an alkanediol, 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 O4:

CxHyO2

Step 1: Draw the structure of the alkane-n,n-diol molecule.

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

C H O

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

Step 8: 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 two hydroxy (or hydroxyl, OH) groups are present, the number of oxygen atoms is 2.

Step 9: Check that your completed molecular formula makes sense (CnH2n+2O2)

Example

Write the molecular formula for butane-1,3-diol (1,3-butanediol).

Step 1: Draw the structure of the alkane-n,n-diol molecule.

  H   H   OH   H  
  |   |   |   |  
HO- 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 oxygen (O).

C H O

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

  H   H   OH   H  
  |   |   |   |  
HO- 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 O

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

  H2   H3   OH4   H5  
  |   |   |   |  
1HO- C - C - C - C -H6
  |   |   |   |  
  H10   H9   H8   H7  

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).

C4H10O

Step 7: Count the number of oxygen atoms in the alkanediol molecule:

  H   H   2OH   H  
  |   |   |   |  
HO1- C - C - C - C -H
  |   |   |   |  
  H   H   H   H  

Step 8: 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).

Two oxygen atoms are present in this molecule, O2

Molecular formula for butane-1,3-diol is C4H10O2

Step 9: Check that your completed molecular formula makes sense (CnH2n+2O2)
n = number of carbon atoms = 4
number of hydrogen atoms = 2 x n + 2 = 2 x 4 + 2 = 10
number of oxygen atoms = 2

Summay Table: Molecular Formula, Structure and Name of Some Alkanediols

no. C atoms
(n)
Molecular Formula
CnH2n+2O2
Structure Name
1 CH4O2
    OH
|
   
H - C - OH
    |
H
   
methanediol

2 C2H6O2
    H
|
  OH
|
   
H - C - C - OH
    |
H
  |
H
   
ethane-1,1-diol
(1,1-ethanediol)
    H
|
  H
|
   
OH - C - C - OH
    |
H
  |
H
   
ethane-1,2-diol
(1,2-ethanediol or
ethylene glycol)

3 C3H8O2
    H
|
  H
|
  OH
|
   
H - C - C - C - OH
    |
H
  |
H
  |
H
   
propane-1,1-diol
(1,1-propanediol)
    H
|
  OH
|
  H
|
   
H - C - C - C - OH
    |
H
  |
H
  |
H
   
propane-1,2-diol
(1,2-propanediol)
    H
|
  H
|
  H
|
   
OH - C - C - C - OH
    |
H
  |
H
  |
H
   
propane-1,3-diol
(1,3-propanediol)
    H
|
  OH
|
  H
|
   
H - C - C - C - H
    |
H
  |
OH
  |
H
   
propane-2,2-diol
(2,2-propanediol)

4 C4H10O2
    H
|
  H
|
  H
|
  OH
|
   
H - C - C - C - C - OH
    |
H
  |
H
  |
H
  |
H
   
butane-1,1-diol
(1,1-butanediol)
    H
|
  H
|
  OH
|
  H
|
   
H - C - C - C - C - OH
    |
H
  |
H
  |
H
  |
H
   
butane-1,2-diol
(1,2-butanediol)
    H
|
  OH
|
  H
|
  H
|
   
H - C - C - C - C - OH
    |
H
  |
H
  |
H
  |
H
   
butane-1,3-diol
(1,3-butanediol)
    H
|
  H
|
  H
|
  H
|
   
OH - C - C - C - C - OH
    |
H
  |
H
  |
H
  |
H
   
butane-1,4-diol
(1,4-butanediol)
    H
|
  OH
|
  OH
|
  H
|
   
H - C - C - C - C - H
    |
H
  |
H
  |
H
  |
H
   
butane-2,3-diol
(2,3-butanediol)
    H
|
  H
|
  OH
|
  H
|
   
H - C - C - C - C - H
    |
H
  |
H
  |
OH
  |
H
   
butane-2,2-diol
(2,2-butanediol)

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1The OH functional group in alkanols is called the hydroxy group or hydroxyl group.
While the IUPAC document refers to the hydroxy group, hydroxyl is also a possible name because of the retention of the unpaired electron on the oxygen atom.
Hydroxide is NOT a possible name for the OH group because the "ide" suffix refers to the gain of an electron, that is, it refers to the negatively charged OH- ion.
Note that when another functional group takes precedence over the OH functional group, the OH group is then named as the hydroxy group.

2IUPAC 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 straight chain alkanols we are discussing, either nomenclature is acceptable since the name in each case is unambiguous.
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

4The molecular formula of an alkanediol is CnH2n+2O2
Condensed structural formulae (or semi-structural formulae) will show the location of the OH functional groups, eg, CH2OH-CH2OH is a condensed (semi) structural formula for ethane-1,2-diol

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