Aldehydes & Ketones

(These are a subgroup of the carbonyl family. Aldehydes are characterized by a Hydrogen atom and a Carbon group attached to the carbonyl. Ketones have the carbonyl attached to two carbon groups.)

Basic IUPAC nomenclature-ALDEHYDES: (See the home page for parent root names, prefixes & suffixes.)

1. Number the longest chain of carbon atoms that contains the carbonyl such that the carbonyl carbon is number 1.

2. Identify the root name of the structure; change the suffix from -e to -al.

The root name of the compound is butane, dropping the -e and changing to -al will give the formal name of butanal. It is not necessary to use the #1 in the name; it is understood that the #1 carbon is, by definition the aldehyde carbon. However, there are two isomers of butanal. This one is the linear or "normal" isomer.

There is also a constitutional isomer of butane, which will have two names-an IUPAC and a common name:

The aldehyde carbon is still numbered #1, but the carbons are branched to form the isobutyl group. This isomer has the common name: isobutyraldehyde. All compounds have an IUPAC name (not all have a common name) and applying the numbering, as shown, the compound is actually named as a propan-  + -al which has a methyl group at position #2. 2-Methylpropanal-is the IUPAC name. Notice, there is no need to use the #1 in the name, since it is understood that the aldehyde carbon is #1 and the numbering of the chain begins there.

3. If the compound contains a double bond i.e. it is also an alkene, then change the infix from -an- to -en-  and the placement of the infix is determined by the numbering.

The 2 Carbon base name of this compound is propane. There are two functional groups present and the name must account for both of them, and a C=O takes precedent over the C=C. So, the base name becomes: propanal. The aldehyde carbon defines position #1; the alkene begins at C#2; the name is: 2-Propenal.

This is a combination frequently found in organic chemistry: the carbonyl and the alkene. It is usually referred to as an a,b-unsaturated carbonyl compound.

The carbon atom connected to the carbonyl is designated the alpha (a) carbon and the second carbon of the double bond is the beta (b) carbon. Thus, the double bond, linking the two carbons is called: a,b. However, the #1 carbon in the system, is still the carbonyl carbon.


4. When the aldehyde functional group is attached to a ring, the entire suffix:-carbaldehyde is used. Examples are:

Cyclohexanecarbaldehyde Cyclopentanecarbaldehyde


5. The IUPAC system retains several common names:

Formaldehyde (derived from formic acid: HCOOH) Acetaldehyde (derived from acetic acid H3CCOOH) Benzaldehyde


Basic IUPAC nomenclature-KETONES: (See the home page for parent root names, prefixes & suffixes.)

1. Number the longest chain of carbon atoms that contains the carbonyl carbon, such that the C=O has the smallest number.

2. Change the -e of the alkane to -one.

3. Cyclic compounds are named in the same fashion; e.g. cyclohexan-  + -one = cyclohexanone.

4. The IUPAC system retains several common names:

Acetone (propanone) Acetophenone Benzophenone

Common Names for Aldehydes & Ketones

1. For aldehydes, common names are derived from their corresponding carboxylic acids:

Formaldehyde (derived from formic acid HCOOH); Acetaldehyde (derived from acetic acid H3CCOOH)

2. For ketones, the two alkyl groups are named, alphabetized and placed in front of the term "ketone":

Diethyl ketone Ethyl methyl ketone Methyl vinyl ketone (MVK) Dimethyl ketone Methyl isopropyl ketone

EXERCISE: Write the IUPAC name for each of the following structures.

Structure Name Structure Name
1 2,5-Dimethyloctanal 6 3-Methylbutanal
2 3-Methyl-4-heptanone 7 4-Phenyl-2-butanone
3 3,4-Dimethyl-3-penten-2-one 8 2-Methylcyclopentanone
4 2-Methyl-2-cyclopentenone 9 4-heptanone
5 2-Cyclohexenone 10 cycloheptanone



email questions & comments to: Dr. JA Colapret