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Naming Simple Esters

Key Concepts

  • An ester is like a carboxylic acid in which the hydrogen atom of the carboxylate functional group has been replaced by an alkyl group1 (a chain of carbon atoms).

    carboxylic acid   ester
      O
    ||
     
    R- C -O-H
     
      O
    ||
     
    R- C -O-R'

  • An ester therefore contains the ester, COO, functional group:

      O
    ||
     
    R- C -O-R'

  • The name of a simple ester is made up of two words separated by a space2:

          (i) The first word is the name of the alkyl group that has replaced the acid's hydrogen atom.

    Names of straight-chain alkyl groups
    No. C atoms 1 2 3 4 5 6 7 8
    name methyl ethyl propyl butyl pentyl hexyl heptyl octyl
    Note the yl ending !

          (ii)The second word is derived from the name of the carboxylic acid:

    Preferred IUPAC Names of straight-chain acid derivatives
    No. C atoms 1 2 3 4 5 6 7 8
    carboxylic acid name formic acid
    (methanoic acid)
    acetic acid
    (ethanoic acid)
    propanoic acid butanoic acid pentanoic acid hexanoic acid heptanoic acid octanooic acid
    acid derivative name formate
    (methanoate)
    acetate
    (ethanoate)
    propanoate butanoate pentanoate hexanoate heptanoate octanooate
    Note that the end of the name changes from oic acid to oate

  • The general form of the name of a simple ester is therefore alkyl alkanoate

Steps for Naming Simple Esters

Step 1: Locate the ester, COO, functional group.

Step 2: (a) Identify the alkyl chain making up the carboxylic acid
Note that the carbon double bonded to the oxygen atom is the first carbon of the carboxylic acid chain.

  O
||
 
R- C -O-R'

            (b) Name this alkanoic acid.

            (c) Change the end of the name from "oic acid" to "oate"

Step 3: (a) Identify the alkyl group that has replaced the H of the carboxylate group

  O
||
 
R- C -O-R'

            (b) Name this alkyl group.

Step 4: Assemble the name by placing the name of the alkyl group before the modified name of the alkanoic acid.

            Remember to leave a space between these two words!

alkyl alkanoate

Example of how to name an ester

Name the ester shown below:

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

Step 1: Locate the ester, COO, functional group.

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

Step 2: (a) Identify the alkyl chain making up the carboxylic acid
Note that the carbon double bonded to the oxygen atom is the first carbon of the carboxylic acid chain.

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

            (b) Name this alkanoic acid.

            2 carbon atoms in the alkanoic acid chain = acetic acid     (ethanoic acid)

            (c) Change the end of the name from "oic acid" to "oate"

            acetic acid → acetate     (ethanoic acid → ethanoate)

Step 3: (a) Identify the alkyl group that has replaced the H of the carboxylate group

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

            (b) Name this alkyl group.

            1 carbon atom in the alkyl chain = methyl

Step 4: Assemble the name by placing the name of the alkyl group before the modified name of the acid.

            Remember to leave a space between these two words!

methyl acetate (preferred IUPAC name)

(methyl ethanoate is systematic but not preferred)

Steps for Drawing the Structure3 of Simple Esters

Step 1: Identify the name of the alkyl group and the name of alkanoic acid from which the ester is derived:

Name of ester
alkyl   alkanoate

Step 2: Draw the structure of the alkanoic acid from which the ester is derived.
Remember that the carbon atom that is double bonded to the oxygen atom is the first carbon atom in the chain.

  O
||
 
R- C -O-H

Step 3: Remove the hydrogen atom that is bonded to the oxygen atom of the carboxylate functional group:

  O
||
 
R- C -O-

Step 4: Use the name of the alkyl group (the first word of the ester's name) to determine how many atoms are in the alkyl group's chain of atoms.

Step 5: Starting from the oxygen atom in the carboxylate group which has lost its hydrogen atom, draw in the chain of carbon atoms required using a dash to represent a covalent bond between carbon atoms:

  O
||
     
R- C -O- C -R'
         

Step 6: Draw dashes around each carbon atom in the alkyl chain to represent covalent bonds such that each carbon atom makes 4 covalent bonds.

Step 7: Complete the structure by placing a hydrogen atom, H, at the end of any vacant dash.

Example of how to draw the structure of an ester

Draw the structure for a molecule of the ester ethyl propanoate.

Step 1: Identify the name of the alkyl group and the name of alkanoic acid from which the ester is derived:

Name of ester
alkyl   alkanoate
ethyl   propanoate

Step 2: Draw the structure of the alkanoic acid from which the ester is derived.
Remember that the carbon atom that is double bonded to the oxygen atom is the first carbon atom in the chain.

Propanoic acid has 3 carbon atoms in the chain, the carbon atom of the carboxylate group is the first carbon atom in the chain.

  H
|
  H
|
  O
||
 
H- C3 - C2 - C1 -O-H
  |
H
  |
H
     

Step 3: Remove the hydrogen atom that is bonded to the oxygen atom of the carboxylate functional group:

alkanoic acid becomes alkanoate
  H
|
  H
|
  O
||
 
H- C - C - C -O-H
  |
H
  |
H
     
  H
|
  H
|
  O
||
 
H- C - C - C -O-
  |
H
  |
H
     

Step 4: Use the name of the alkyl group (the first word of the ester's name) to determine how many atoms are in the alkyl group's chain of atoms.

Ethyl group is a chain of 2 carbon atoms with a single covalent bond between them.

Step 5: Starting from the oxygen atom in the carboxylate group which has lost its hydrogen atom, draw in the chain of carbon atoms required using a dash to represent a covalent bond between carbon atoms:

  H
|
  H
|
  O
||
       
H- C - C - C -O- C1 - C2
  |
H
  |
H
           

Step 6: Draw dashes around each carbon atom in the alkyl chain to represent covalent bonds such that each carbon atom makes 4 covalent bonds.

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

Step 7: Complete the structure by placing a hydrogen atom, H, at the end of any vacant dash.

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

Steps for Writing the Molecular Formula of Simple Esters

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

For a simple ester, only three elements are present, carbon (C), hydrogen (H) and oxygen (O).

When writing the molecular formula of a simple ester, 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.
A simple ester will always have 2 oxygen atoms.

CxHyO2

Step 1: Draw the structure of the ester 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 ester 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 ester 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 ester 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).

Example of writing the molecular formula of an ester

Write the molecular formula for the ester ethyl formate (ethyl methanoate).

Step 1: Draw the structure of the ester molecule.

  ethyl
  O
||
  H
|
  H
|
 
H- C -O- C - C -H
      |
H
  |
H
 
formate
(methanoate)
 

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 ester molecule.

  O
||
  H
|
  H
|
 
H- C1 -O- C2 - C3 -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).

C3H O

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

  O
||
  2H
|
  3H
|
 
1H- C -O- C - C -H4
      |
H6
  |
H5
 

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).

C3H6O

Step 7: Count the number of oxygen atoms in the ester molecule.

  1O
||
  H
|
  H
|
 
H- C -O2- C - C -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).

C3H6O2

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

no. C atoms
(n)
Molecular Formula
CnH2nO2
Structure Preferred IUPAC Name
(alternative name)
2 C2H4O2
  O
||
  H
|
 
H- C -O- C -H
      |
H
 
methyl formate
(methyl methanoate)

3 C3H6O2
  H
|
  O
||
  H
|
 
H- C - C -O- C -H
  |
H
      |
H
 
methyl acetate
(methyl ethanoate)
  O
||
  H
|
  H
|
 
H- C -O- C - C -H
      |
H
  |
H
 
ethyl formate
(ethyl methanoate)

4 C4H8O2
  H
|
  H
|
  O
||
  H
|
 
H- C - C - C -O- C -H
  |
H
  |
H
      |
H
 
methyl propanoate
  H
|
  O
||
  H
|
  H
|
 
H- C - C -O- C - C -H
  |
H
      |
H
  |
H
 
ethyl acetate
(ethyl ethanoate)
  O
||
  H
|
  H
|
  H
|
 
H- C -O- C - C - C -H
      |
H
  |
H
  |
H
 
propyl formate
(propyl methanoate)

5 C5H10O2
  H
|
  H
|
  H
|
  O
||
  H
|
 
H- C - C - C - C -O- C -H
  |
H
  |
H
  |
H
      |
H
 
methyl butanoate
  H
|
  H
|
  O
||
  H
|
  H
|
 
H- C - C - C -O- C - C -H
  |
H
  |
H
      |
H
  |
H
 
ethyl propanate
  H
|
  O
||
  H
|
  H
|
  H
|
 
H- C - C -O- C - C - C -H
  |
H
      |
H
  |
H
  |
H
 
propyl acetate
(propyl ethanoate)
  O
||
  H
|
  H
|
  H
|
  H
|
 
H- C -O- C - C - C - C -H
      |
H
  |
H
  |
H
  |
H
 
butyl formate
(butyl methanoate)


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1Compounds derived from carboxylic acids are generally referred to as acid derivatives.
In terms of nomenclature, this replacement of the hydrogen atom is considered a functionalisation rather than a substitution.
For this tutorial, we will only be concerned with examples where the hydrogen atom has been replaced by an alkyl group (that is a group derived from the alkane series).
And, we only be dealing with esters derived from straight chain carboxylic acids, so the name of the ester will be two words.
It should be noted that the names of more complex esters will be made up of more than 2 words.
If more than organyl group (alkyl, aryl etc) is present, they are cited in alphabetical order.

2IUPAC preferred nomenclature for esters follows functional class nomenclature rather than substitutive nomenclature. This results in ester names made up of two words instead of one.However, if branches or other substitutions are present on an alkyl chain within an ester, these branches are named using substitutive nomenclature.
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 a simple ester is CnH2nO2, while the often used CxHyCOOCaHb is, strictly speaking, not a molecular formula but a condensed structural formula.

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