Nomenclature
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Nomenclature

IUPAC Names

The naming of ketones is actually fairly simple, if you use the IUPAC method. It is very similar to the naming of alcohols. You start by choosing the longest carbon chain you can find that includes the carbon from the carbonyl group and use the length of that carbon chain as your base name. You change the ending by removing the -e and adding -one, and adding a number at the beginning of the name to indicate which carbon is double bonded to the oxygen. Then, if there are any side groups attached to the main chain, those are added to the front of the name with the appropriate numbers to show their location.

Example

A specific example is shown here (from Example 12-b in your workbook): butanone is formed from 2-butanol. The carbon chain is four carbon atoms long. Therefore, we have "butane" as a starting point. One of those carbons is double bonded to an oxygen. This make the compound a ketone. This means that we replace the -e ending on the "butane" with an -one ending to get butanone. (We could also use a 2- in front of this name to indicate that it is the 2nd carbon which is a member of the carbonyl group. This gives the name 2-butanone for this particular compound.  However, the 2- is unnecessary here since if the carbonyl group were to be moved one carbon to the right we would start numbering from the right side of the compound and that carbon would be #2.)
H   H H
|   | |
H-C-C-C-C-H
| || | |
H O H H

butanone

 

In this example I would also like to point out that the alcohol we start with, and the ketone we end up with both have the same number of carbon atoms. In addition, the carbonyl group in the ketone is in the same location as the hydroxyl group in the alcohol. This is a very important consideration when you are trying to make a particular ketone. You need to start with an alcohol that has the same arrangement of atoms and has the hydroxyl group in the place that you want the carbonyl group to end up.

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

2-butanol

K2Cr2O7
¾¾¾¾¾¾®
H2SO4, heat

 

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

butanone

 + 2[H]

 

Practice

I would like you to try your hand at using this IUPAC method for naming ketones by naming the ketones for which the structural formulas are given below. Then figure out the structural formulas for the names that are given below. (These are also shown in Exercise 15 in your workbook) . Please take a moment now to figure out the names and structural formulas for these compounds, then check your answers below before continuing.

H H   H H
| |   | |
H-C-C-C-C-C-H
| | || | |
H H O H H
H  
|  
H-C-H  
|  
H  |  O  H
|  |  ||  |
H-C--C--C--C-H
|  |     |
H  H     H
2-pentanone
3,4-dimethyl-2-heptanone

 

Answers

H H   H H
| |   | |
H-C-C-C-C-C-H
| | || | |
H H O H H		 3-pentanone
H  
|  
H-C-H  
|  
H  |  O  H
|  |  ||  |
H-C--C--C--C-H
|  |     |
H  H     H		 3-methyl-2-butanone
2-pentanone H   H H H
|   | | |
H-C-C-C-C-C-H
| || | | |
H O H H H
3,4-dimethyl-2-heptanone H      CH3 CH3 H  H  H
|     |   |  |  |  |
H-C--C--C---C--C--C--C-H
|  ||  |   |  |  |  |
H  O  H   H  H  H  H

 

Common Names

You also need to know that there is another way to name ketones. This is so that when you see a name like methyl ethyl ketone, you will be able to understand what that name represents.

That method of naming ketones involves this. You take the carbonyl as the ketone group and then you look at what kind of alkyl groups are attached to that carbonyl group. You name the ketone by naming each of those alkyl groups and then say "ketone."

R-C-R'
||
O
2-Pentanone, for example, has a carbonyl group with a methyl attached on one side and a propyl attached on the other. Thus it could be called methyl propyl ketone.

H   H H H
|   | | |
H-C-C-C-C-C-H
| || | | |
H O H H H
This compound has a ketone group to which is attached a methyl group and an isopropyl group. Therefore it could be called methyl isopropyl ketone.

  H   CH3
|   |
H-C-C-C-H
| || |
  H O CH3

 

Also notice that these names are written as three separate words, whereas all of the IUPAC names have been continuous, no spaces, one word.

 

Practice

With that much information I would like you to draw the structural formula for methyl ethyl ketone and then figure out the IUPAC name for that compound (Exercise 16 in your workbook).

 

Answer

H   H H
|   | |
H-C-C-C-C-H
| || | |
H O H H
butanone
People who use this compound a lot give it the abbreviated name of MEK.

 

More Practice

If you want, you might try to come up with similar names for the compounds shown below. These are the same ones you worked with earlier. (They are also shown in Examples 15-a, b, and c. However, don't try 15-d. This method works best for fairly simple ketones.)

H H   H H
| |   | |
H-C-C-C-C-C-H
| | || | |
H H O H H
H  
|  
H-C-H  
|   
H  |  O  H
|  |  ||  |
H-C--C--C--C-H
|  |     |
H  H     H
2-pentanone

 

 

 

Answers

H H   H H
| |   | |
H-C-C-C-C-C-H
| | || | |
H H O H H		 diethyl ketone
H  
|  
H-C-H  
|   
H  |  O  H
|  |  ||  |
H-C--C--C--C-H
|  |     |
H  H     H		 methyl isopropyl ketone
2-pentanone H   H H H
|   | | |
H-C-C-C-C-C-H
| || | | |
H O H H H

methyl propyl ketone

 

Acetone

In addition to all of this, there is one more common ketone name that you need to learn (memorize). It is acetone. Acetone is the smallest of the ketones. It has three carbon atoms. You will draw its structural formula when you do part II of the experiment.

 

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E-mail instructor: Eden Francis

Clackamas Community College
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